insects, the larvae do not move at first when a flashlight is directed at them: this does not say they lack light perception; but their eyes probably only function as sense organs suitable to let them know when night has fallen, and dawn has come. The glow-worms do not see as well as the larvae of the tiger beetle, which live in holes in clay banks. The glow-worm depends on its snare, the tiger beetle larva on its sight and quickness.

The Gut of the Larva.

In Pl. 24, Figs. 5 and 6, are the parts of the gut, as seen when the last segment is cut off and the viscera pulled out by the head. The oesophagus (O) is markedly contractile. The chocolate coloured diverticula (D) show muscular movements, not apparently peristaltic, but such as would be produced by contraction of scanty circular muscles. No doubt it is by such contractions that the mucous droplets are expelled at intervals from the mouth, as the snare is being constructed. Owing to the position of emergence of the diverticula from the oesophageal valve, the latter probably controls the issue of mucus. The oesophageal valve is yellow in colour.

The mesenteron was never found quite empty in newly caught specimens, but if the larvae are starved for several days, the gut contents move down leaving the upper part empty. Food was never found in the intestine (IN) except on one occasion when the digested material was observed in the lower part of the mesenteron; it quickly passed through into the intestine and was immediately voided. The food contents seen in the mesenteron always appeared brownish. Recently a larva was seen to regurgitate a drop of food. In Pl. 24, Fig. 5, the four parts of the malpighian tubes (1–4) are shown. The first part (1) is yellowish and hyaline, the second and longest part (2) is of a larger bore, very opaque, and has a pink colour in direct light. The third part (3) very gradually passes into a thinner and more transparent region of part (4); this region is usually disposed in a zigzag fashion, covered with thin connective tissue, and provides the necessary extensile region needed as the animal contracts and lengthens quickly as it moves along; part (4) is the swollen luminescent organ, which, like the lowest part of part (3), is transparent and yellowish. The reflector is glistening white, and when cleared of attachments rapidly floats to the top of the water in the dissecting dish, resembling a tiny boat. These regions of the gut are depicted at a higher magnification in Pl. 24, Fig. 6. When the tubule is pulled out from the living animal, one occasionally sees some of the granules from part (2) passing into the lumen of part (1). It is this process which, before pupation, leads to the adult malpighian tubes being cleared of all the excretion granules collected during larval life. The adult's malpighian tubes are like part (1) of the larval tubes. Part (1), of course, leads into the gut proper. The urine (?) granules in part (2) gradually become less and less towards the distal end, until the cells become hyaline Cross sections of the region (3) reveal that the cells do not always occupy the complete area of the tubule, one side here and there showing a gap, as in Pl. 24, Fig. 6A. This is also shown in Pl. 1, Fig. 5 (C), of the paper by Gatenby & Ganguly (1958). The significance of this method of packing the cells is not known At the region at part (3A) in Pl. 24, Fig. 6, the lumen is still patent, but it appears to be shut off at (LN) by an area of about three cells in length. No granules were ever seen inside the lumen of the living luminescent organ.

In Pl. 24, Figs. 5 and 6, at CT, the connective tissue binding of part (3) and (3A) is drawn in diagrammatically to show that this region is so completely bound that the intestine and the four lower parts of part (3) cannot usually be separated without breaking. In Pl. 24, Fig. 5, the proportionate length of the meanderings of part (3) are not fully shown. A less diagrammatic drawing of this region in an extended animal is shown in Pl. 25, Fig. 7 (CT and M).

The silk glands extend far down to the mid region, and then each one turns up at its lower part (SI) in Pl. 24, Fig. 5. Fat cells (F) are closely bound to the silk glands.

Tracheal System.

In Pl. 23, Fig. 1, is a semi-diagrammatic plan of the tracheal trunks. There are two main tubes (L, L) passing from a fork which goes to head and brain, right down to the reflector and luminescent organ (LO). On the way down these give off branches (T, T) to the viscera. The main trunk leaving the reflector (LO) branches forward (lower T). At intervals the main trunk receives tubules (B) which have branched under the integument at each site. There are no tracheal openings to the exterior, the system being apneustic.

In the pupa, Pl. 23, Fig. 2, there are at least six tracheal openings, each in the mid region of the segment. A higher power drawing of one of those is given in Pl. 23, Fig. 3, the opening at TA, longitudinal trunk at L.

The tracheal system of the imago has not been studied but is probably normal for the family.

The Luminescent Organ.

In Pl. 27, Fig. 12, is a good photograph of the light organ (LO). There are four tubes seen in transverse section in Pl. 26, Fig. 9. In this region the reflector (R) lies underneath, and the tubes are not bound to this, but lie in depressions in the reflector. The intestine and rectum (IN) also lie free, but as far as can be ascertained, the light organ itself is not free to move up or down according to the position of the connectives (CT), and the contraction and relaxation of the longitudinal muscles (LM). The light organ is shown well at (U) in Pl. 27, Fig. 10, the lumen more clearly at (LO) in Pl. 27, Fig. 12. Although the light given by small larvae appears to be bright, their luminescent organ is comparatively small. In Text-fig. 4 (A), is an outline of the adult larval organ, in (B) that of a larva 5 mm in length.

The living cells of the light organ are hyaline and free from granulation except for mitochondria packed in the cytoplasm of the cell.

Lengths of Parts of the Viscus of the Larvae, Etc.

Oesophageal valve, 1.25 mm; silk glands, 22 mm; mesenteron, 10 mm; gut diverticulum, 12 mm; malpighian tube, yellow region (part 1), 2.5 mm; pink region (part 2), 9 mm; (part 3A, difficult to measure); luminescent organ, 0.9 mm; altogether about 15 or 16 mm. This, from typical larvae, but the lengths in some cases obviously depend on the amount of stretching and size of larvae.

The writer's drawings had to be made mostly freehand, as no camera lucida was available at the time. The average larva was about one inch (25 mm) long. One from Waipu, apparently a male, nearly ready to pupate, that is with imaginal discs and visible gonads, was only ¾ inch (19 mm), yet another from the same cave was 1 ¼ inches (about 30 mm) long, and it had no visible imaginal discs in whole mount.

Nervous System.

The nervous system consists of the larger cerebral ganglia (brain), para-oesophageal commissures and sub-oesophageal ganglia, the usual double ventral cord, three ganglia in the three thoracic segments, and a ganglion just behind each abdominal segment, except in that segment containing the light organs. The brain lies just behind the head capsule, not inside it (Pl. 25, Fig. 7B, BR). In Pl. 25, Fig. 7A, are the last three segments, and the supply to the region containing the light organs (LO) comes from the ganglion (NA) in the penultimate segment. This ganglion sends down a nerve which soon branches, one part to the muscles, the other continuing down to the region of the light organs and anal papillae. One

branch (N) certainly comes from the scolophore organs, but it is difficult to follow the paths of the other small branches, some of which go to muscles. This means that it is not presently possible to say whether the central and the sympathetic visceral systems are brought down into the posterior part of the malpighian tubules which are the light organs, and to the reflector. In any case a cut anywhere below the letters (NA) in Pl. 25, Fig. 7A, will isolate the central nervous system and its anterior sense organs, from the light organs. Such a cut will also isolate the posterior part of the haemocoele from any possible hormonic influence arising in front parts of the nervous system, but it will shut off the oxygen supply arising from the segmental tracheole branches beneath the integument. The long tubular heart passes back to just near the border of the last segment. Thus the cut will also interrupt the heart, but will leave a portion of variable length according to the level of the cut below the ganglion (NA) in Fig. 7A. With these difficulties in view a few experiments were made.

Experiments on the Control of Luminescence.

On Pl. 23, Fig. 4, the arrows X, Y and Z show where a cut was made or a nylon thread was tied. The thread was Size A, white, Coats and Clark's, was fine enough for the experiments, and is very strong. Three main types of experiments were tried.

• (1) A tie or cut behind the head, isolating the head from the rest of the body. Head cut off in all cases.

• (2) A tie or cut between X and Y, usually in front of Y, body cut off.

• (3) A tie or cut at Z, isolating any nerve ganglia from the light organ, the body being removed.

It was very difficult to get a thread on to a struggling lighted up larva, before it doused. In (1) and (2), the larva could douse. In (3) the piece below Z, could not douse, and if the experiment was carried out on a doused larva, the luminescent organ lighted up immediately. If (2) was tried on a doused larva, it did not light up, but if (3) was then carried out, it lighted up If the lighted up piece (teased or not) from experiment (3) be covered with blood from a doused larva, it still continues to light up.

From these experiments it appears that the light is kept doused by the posterior ganglion in segment 7. In all cases the light does not turn off or come on suddenly, from which it may be concluded that some other organ is implicated, but not a humoral effect or hormone in the haemocoele fluid. It is likely, but there is no evidence, that the ganglion in segment 7, in some way prevents air from the tracheal reflector from diffusing to the light organ.

Before any conclusion can be drawn, the nerve supply to the light organs and tracheal basket must be examined, but suitable gold or silver preparations have not been made.

In the case of those glow-worms living outside on banks, at present it seems likely that the approach of evening is registered by the eyes of the larva, and a stimulus is sent down from the brain via the ventral nerve cord to the posterior ganglion, which then lifts the block which hitherto has kept air from diffusing across the small gap between the reflector and the light organs. The blood containing air from the reflector could be removed by contraction of the last segment, the swelling or contraction of which is entirely under the control of the larva. Note that in Pl. 23, Fig. 4, this segment is largely contracted, while in Pl. 25, Fig. 7, it is suffused with blood. The writer feels that this is in some way concerned with dousing.

Many attempts were made to dissect the posterior ganglion so that the nerve fibres could be followed to their end organs, but the cuticle was so tough that the task was beyond the skill and patience of the writer The question of the use of the eyes for the perception of night and therefore of lighting-up, was not solved.