the gravelly bed of such rivers as the Selwyn, in Canterbury, and the Otapiri River, and others unnamed, in Southland.

In life, P. pulealis is clongated, slender, rather flattened, with a lateral lobe extending outwards on each side of the oral opening. This opening is slightly raised on an oral flange and is generally visible except when retraction takes place. Locomotion seems generally to be by ciliary action. Cilia have been observed laterally along the whole length, and the movement of particles on the dorsal surface, along with the smooth gliding motion of the whole body, suggests that the whole surface is ciliated. Violent changes of shape

Fig. 1A.—Prorhynchus putcalis Fig. 1B.—P. hasuelli. Figures roughly proportionate, both from life. F., flange on outside of vertical lobe; g. gut; ph., region of pharynx; ten., tentacle.

during gliding are not usual, except that the anterior end may become enormously extended, the pharyngeal region elongating to the length of the rest of the body.

During the excavation of trout redds in the Selwyn River, and later in the Aparima and Otapiri Rivers, in Southland, another Prorhynchus was discovered. This is very much stouter than P. putealis and is clearly a distinct species. In life, it is eyeless, white, very muscular, and shows no sign of external ciliation. It produces slime copiously, and progress is achieved by strong extensions and contractions very different from what was seen in P. putealis. The extended length has been seen in life to be 3 cm., with a diameter of 0 5 cm., but a preserved specimen from the Aparima River is 4 cm. long by 0 5 cm. thick, and shows clear signs of having been contracted. In the contracted condition, the surface is well rounded, with a flange running laterally along the whole length.

Anteriorly there is a sharp difference from P. putealis. There are two forwardly running vertical lobes, each having outside a short horizontal flange continuing forward from the longitudinal lateral flange and reaching not quite to the front edge of the vertical lobe. On the front margin of each vertical lobe is a short tentacle which is completely retractile into a deep pit when the lobe is drawn inward to reduce the mouth opening. The oral opening lies at the base of the U-shaped recess formed by the anterior lobes, and is reduced to a very fine pore when full contraction takes place. Below is the male pore.

Internal Anatomy.

When stained with mucicarmine, mucihaematin or thionin. sections of this second Prorhynchus are strikingly marked by numerous large, deep-seated gland-cells in the parenchyma, laterally to the gut, circular or ovoid in shape, which are more or less successfully traceable through the outer muscular layers as very thin ducts dilating in the ectoderm and opening outwards through fine pores. In Fig. 2, there are only a few representations of the distal portions. but the sections of the ectoderm are massively stained through the mucin-ducts therein contained. The deep-seated portions of the gland-cells are nucleated and clearly belong to the ectoderm. At the same time, the superficial layer of the body contains numerous nuclei. Steinboeek and Reisinger (1924, p. 443) state that the ectodermal nuclei of P. putealis have sunken with part of the protoplasm under the muscular layer, and Hickman (1933, p. 259) says that the eetodermal nuclei of P. tasmaniensis have sunken into the parenchyma below the muscular layers. In my sections of P. putealis, the outer layer of cellular material is extremely thin and rather indefinite, and some nuclei lie sparsely scattered throughout the outer layer of longitudinal muscles. Thus, the present organism differs from the other two mentioned in having an ectoderm containing nuclei outside of the musculature, other parts of it satisfying the requirements of an “eingesenktes epithel.” This external layer is about 0.18 mm. thick and, as already mentioned, is very largely made up of the terminal portions of vast numbers of ducts of glandular cells lying in the parenchyma. The ducts open on the surface through a thin cuticle, or some layer which is distinct from the subjacent tissue.

Musculature.

As shown in Fig. 2. there are two layers of muscles outside of the parenchyma, a compact sheet of circular fibres enclosing a thicker, compact sheet of longitudinal fibres. Neither of these layers shows the bundling of fibres. There are also dorso-ventral muscle fibres passing between the upper and lower surfaces of the lateral regions. The musculature of the pharynx is somewhat similar to that of the other two species in that there are the following layers (Fig. 2a), an outer sheet of longitudinal fibres immediately enclosing a slightly thicker sheet of circular fibres, a broad zone containing nucleated bodies with next inside a thick layer of circular fibres surrounding a zone of radially arranged bundles of longitudinal fibres. The cuticular lining of the proboscis rests on this last layer. Running radially between the radial bundles are bundles of radial fibres reaching to the outermost longitudinal muscular sheet. Again, passing through the thickness of the wall are oblique fibres generally diverging above and below towards the same side. Altogether the pharynx is a massive, muscular organ and maybe two-fifths of the length of the fixed animal.

Alimentary Canal.

The gut system is essentially the same as that of the other species. The proboscis is attached along its length to the parenchyma by a sheath of loose connective tissue. Only a very short anterior portion is free, the tube sliding to and fro in the loose sheath. Five to seven lateral pouches have been found on each side of the gut, formed by the inward extension of septa of fibrous connective tissue continuous with a fibrous layer covering the greater part of the gut (Fig. 2a, s.).

Evidently considerable secretion takes place in the endoderm cells, as masses of granules are brought to view by Heidenhain's haematoxylin and by Mallory's triple stain.

There is an antero-ventral pouch below the hind end of the proboscis, as in P. putealis, and P. tasmaniensis, and over the whole surface of the gut, following the undulations caused by the septa, is a layer of longitudinal muscle fibres. With Mallory's triple stain, these fibres appear to be continuous with the bases of the endoderm cells, leading to the conclusion that the endoderm forms a musculoepithelium. Haswell (1898, p. 637) refers to a layer, “apparently muscular,” present (presumably) outside the endoderm of P. putealis. In this latter species, the gut musculature is not so well developed as in the species under description. Hickman does not mention a sheet of muscles covering the gut of P. tasmaniensis. The powerful gut muscles must play a considerable part in churning the food contained, in addition to the action of the musculature of the body wall.

Nervous System.

The general arrangement of the nervous system is as described in the other two species. Some aspects are, however, worthy of some fuller treatment. While the transverse, horse-shoe shaped band of fibres lying above and somewhat in front of the anterior end of the proboscis is well marked, there are less clearly-defined bundles passing between it and the antero-dorsal and dorso-lateral

tip. These bundles lie in a large mass of nucleated cells forming a very considerable portion of this anterior region of the body and having the total character of a ganglionic mass. The large, transverse band is traceable back as a pair of middle longitudinal trunks (Fig. 2, n.m.l.). The dorso-lateral trunks are traccable back as independent cords from the ganglionic mass, while the ventro-lateral cords separate from the middle longitudinal trunks shortly after these latter become defined. Throughout the proboscis, in the nucleated region, are visible irregular nerve cords which are generally traceable to two lateral cords alongside and external to the proboscis and its sleeve of connective tissue and rising from the middle longitudinal trunks further forward. A pair of outer trunks, the lateral longitudinal trunks of Steinboeck and Reisinger, has not been clearly identified, but in the dorsal side of the body flange, immediately between the circular muscles and the ectoderm, is a thin band of varying width of unstained material which may be regarded as a very thin sheet, but its relation with the main trunks has not been determined.

Excretory System.

Little need be said about this system as it conforms to the descriptions of the other two species. The pores lie ventrolaterally in a transverse plane about half way between the front of the anteroventral diverticulum of the gut and the posterior end of the proboscis.

Reproductive System.

It has not yet been possible to find fully mature specimens of this animal, but one advanced in maturity and two much less mature have been examined.

In the advanced specimen the general arrangement of the genital structures is much like that in the other species from New Zealand and Tasmania, but details of difference are sufficiently sharp. The sacculate testes lie on the right side of the gut, nearly as far forward as the hind end of the pharynx, at first as a slender series of follicles (Fig. 3). With growth, the follicles extend upwards and downwards, forming a sheet from ventro-lateral to dorso-lateral, and running about the length of the gut. In the most mature specimen, vasa efferentia were clearly visible passing from the testicular sacs to the vas deferens, but the sacs contained only undifferentiated cells, some of which showed mitotic figures.

The vas deferens ultimately passes forward and under the fore part of the enteron, to form a median ventral convoluted tube having a wall of large cells and a well-defined lumen. It passes forward without dilatation to form a tube having a fibrous (? muscular) wall, similar in position and character to the vesicula granulorum, and leading directly into the penis.

The lumen of the penis is contained in an apparently chitinous tube. Outside this tube is a fibrous sheath, continuous with the fibrous sheath behind (? vesicula granulorum), and having longitudinal fibres between it and the chitinous tube. The interpretation of these structures is that there is a not well developed vesicula granulorum with a muscular wall which is continued over the penial

Fig. 3.
Prorhynchus haswelli. Diagram showing essential features of male and female reproductive systems and their relations the one to the other. c., caecum of female duct; g.i.c., genito-intestinal canal; g.p.f., female genital pore; g.p.m., male genital pore; gv., germo-vitellarium; int., gut; o.m., outer mautle of penis; st., stilctto of penis; t., testicular follicle; v.d., vas deferens; v.e., vas efferens; v.g., vesicula granulorum.

chitinous tube as an outer layer of sinistral spiral fibres outside a layer of longitudinal muscle fibres. This penial complex is attached at its base to a further sheath, as has been described in the other species, but the sheath appears otherwise free, both in longitudinal and transverse sections, indicating that the inner apparatus slides freely inside the sheath. This outer sheath is provided with 16 chitinous slender rods and is slightly longer, terminally, than the enclosed tube. A small anterior portion of the outer sheath is free from the surrounding body, but the rest is bound by connective tissue. The total length of the penial structure is about 1.0 mm. Steinboeck and Reisinger (1924, text fig. 3) show a well-defined penial protractor muscle in P. stagnalis, and Haswell (1898, Pl. 48, Fig. 5) shows a similar clearly figured musculature in P. putealis. In the present case, although there is a very considerable musculature, chiefly longitudinal, connected with and outside the penis, there are no well-defined bands. Whether or not they become so later must remain uncertain until a mature animal is found.

Steinboeck and Reisinger (1924, text fig. 4) provide very clear figures illustrating “the function of the male apparatus of Prorhynchus”. There the terminal male duct is shown to open into a common oro-genital canal: such a condition is found in P. putealis. In the present case, however, there is a well developed horizontal septum lying between the oral opening and the penial pore, quite thick at

its edge, separating a thin, more ventral flap, on which opens the fine penial duct, from the proboscis tube: thus there is not yet seen an oro-penial duct.

The female reproductive apparatus consists of a long, convoluted germo-vitellarium lying at first mid-laterally on the left of the gut. The duct appears later in development, passing downwards towards the middle line where it meets a genito-intestinal canal which originates ventrally in the gut immediately behind the third septum. These two ducts pass forward together to join beneath the gut, between the second and third septa. Shortly before the common duct passes into the female pore, which lies approximately in the same transverse plane as do the excretory pores, and mid-ventrally, it receives a further duct which arises blindly in the connective tissue of the first septum and passes under and across from the left, lying in the fibrous connective tissue coat covering the gut and in which also lies the oviduct. The wall of this blind duct resembles in structure the wall of the oviduct in the same region, large cells, and fine, slender lumen, but there is nothing present from which an indication can be gathered about its function. This may be better determined at sexual maturity. At the present stage of development, the female genital antrum is not apparent.

Prorhynchus haswelli Steinboeck and Reisinger.

Steinboeck and Reisinger (1924) refrained from a full description of P. haswelli, the fourth of Haswell's specimens, concerning themselves particularly with referring to the “Epithelmuskelzellan” and the large nuclei. Although the cuticular parts of the stiletto were present, there was neither description nor figure. However, the examination of this large, bulky prorhynchid found in company with P. putealis, leads to the conclusion that it is Prorhynchus haswelli, sufficient detail being available to distinguish it sharply from P. putealis and P. tasmaniensis. Externally, it is characterised by the two large anterior lobes, each bearing a small retractile tentacle. Internally, it is peculiar in its few gut caeca (5 to 7), and the gut cells do not form a syncytium. The actoderm external to the outer, circular muscles contains numerous nuclei, the parenchyma contains the inner ends of many large, striking mucin-secreting gland cells, these alone distinguishing the section from that of P. putealis. The testes, folliculated, are on the right of the gut, along its length, as in P. tasmaniensis (it is here confirmed that the testes are on the left in P. putealis), the stiletto is in the form of a long, cuticular tube, and the sheath has 16 rods, there being 10 in P. tasmaniensis. No inner mantle (of the penis, cf. Steinboeck and Reisinger, p. 446 and text fig. 3, i.m.) has been found. The male pore opens below, but not into the proboscideal sheath.

Extended Description of Prorhynchus haswelli Steinboeck and Reisinger:

Large (up to 4cm. long), white, blind with two anterior, vertical lobes each bearing a small retractile tentacle on each side of the oral opening; five to seven gut caeca on each side; testes on the right side, germo-vitellaruim on the left side of the gut, with genito-intestinal canal connecting gut and