appears black toward its periphery in the photographs. In still water the eggs float to the surface owing to the buoyancy of the oil glouble which occupies the upper pole of the sphere.

Half an hour after milt has been added to the eggs (Plate 23, Figure 1) the protoplasm is differentiated from the yolk to form a circular germinal disc, 0.5 to 0.6 mm in diameter around the lower pole. The egg membrane, which is seen in optical section, appears as a dark outline outside and concentric with the germinal disc, and is not to be confused with the edge of the circular field of view commonly shown in photomicrographs. In the photograph the camera is vertical and is focused on the lower surface of the egg, so that the oil globule appears slightly out of focus. By adjusting the convergence of the illumination or throwing it slightly off centre the presence of minute inclusions may be detected in the yolk and germinal disc, particularly the latter. Plate 25, Figure 1, shows the same stage from an oblique view point so that the germinal disc is seen in profile. Although the germinal disc has been displaced toward the lower edge of the photograph in this and other oblique views taken with the vertical camera, the oil globule retains its position in the centre of the circle described by the egg membrane. It would appear from this that the yolk is in a semi-fluid state, so that when the egg is rotated round a horizontal axis the oil globule is able to move to the uppermost point of the sphere, provided the angular distance travelled is not greater than about 80 degrees. After an hour (Plate 23, Fig. 2) the first cleavage has been completed, giving two distinct elliptical blastomeres. In this figure the minute inclusions in the protoplasm may be seen. These become less evident as development proceeds. In 1½ hours the second cleavage has taken place at right angles to the first (Plate 23, Fig. 3). Both this and the following figure show clearly the tendency of adjacent walls of blastomeres to coalesce along the cleavage plane, so that the most recent cleavage may be identified by the deeper indentation at the edge of the germinal disc. The first two cleavage furrows pass more or less vertically through the blastoderm, so that the four blastomeres are very clearly defined, although still incompletely separated in their deeper portions.

A third cleavage parallel to the first has taken place after 2 hours, producing an 8-celled stage (Plate 23, Fig. 4), while in 2½ hours a fourth cleavage parallel to the second gives 16 blastomeres (Plate 23, Fig. 5). The furrows by this time are less clearly defined, since the third and fourth cleavage planes curve inward beneath the surface of the blastoderm to intersect the first and second furrows, thereby splitting the blastoderm into two layers. In Plate 25, Fig.2. an oblique view shows the edge of the blastoderm at 2⅔ hours in the process of cleavage between 16 and 32 cells.

At 3 hours the surface pattern of the 32-celled stage (Plate 23, Fig.6) is becoming obscure owing to the two-layered structure, the deeper layer being still a continuous sheet of protoplasm, while the superficial layer is divided into distinct cells. By 3½ hours (Plate 23, Fig.7) the blastoderm, now with 64 cells, is becoming roughly circular, while the regularity of the cleavage pattern is being lost. Cell division now continues at approximately half-hour intervals until at 6 hours (Plate 23, Fig. 8) the blastoderm has become a multiple-layered cellular plate, still undifferentiated and with individual cells still visible after about 11 cleavage. A lateral view of the same stage (Plate 25, Fig.3) shows the position of the egg as it floats in the water with the oil globule uppermost and

the blastoderm beneath. The blastoderm is still of approximately the same dimensions as the original undivided germinal disc.

Ten hours after fertilisation (Plate 23, Fig. 9) the blastoderm, which is still radially symmetrical, has spread over the surface of the yolk till its diameter is about 0.8 mm. while the germ ring first appears as a slight thickening in the deeper layer at the periphery of the blastoderm. One hour later (Plate 23, Fig. 10) the germ ring is more clearly defined, and part of it is beginning to spread toward the centre of the blastoderm, forming the embryonic shield at what will later become the posterior extremity of the egg. At 12 hours (Plate 23, Fig. 11) the embryonic shield has enlarged still more, while the blastoderm edge opposite is extending towards the equator of the egg. Plate 25, Fig. 4 is an oblique view of the same stage showing how the shape (but not the volume) of the original disc has changed. In another hour (Plate 23, Fig. 12) the blastoderm has spread beyond the equator of the egg and is almost hemispherical.

In Plate 24, Fig. 1. at 15 hours the blastoderm is still spreading rapidly until at 17 hours (Plate 24, Fig. 2) the surface of the yolk is almost completely enclosed, leaving exposed only a circular yolk plug about 0.5 mm in diameter. The embryo now appears as a slight folding and thickening of the blastoderm in the lower hemisphere of the egg, while at 18 hours the head has begun to take shape, although the caudal extremity is still little differentiated (Plate 24, Fig. 3). Plate 25, Fig. 5 is a posterior view of the egg at the same stage, the camera being focused on the yolk plug, so that the head on the far side of the egg is slightly out of focus, though it is clearly seen projecting up toward the centre of the photograph. The blastodermal rim is circular in shape except where it is interrupted by the undulating edge of the caudal swellings. Figure 6 is a lateral view showing the thickened edge of the blastoderm and the pro-truding yolk plug immediately above the caudal extremity of the embryo.

At 20 hours (Plate 24, Fig. 4) the embryo is distinct throughout its length, with the optic lobes just beginning to appear on the head, while the caudal swellings show prominently on either side of the posterior extremity. At 22 hours (Plate 24. Fig. 5) the optic lobes have increased in size and the myotomes are beginning to form, while the caudal swellings are no longer apparent. There is little change in the general appearance of the embryo at 24 hours (Plate 24, Fig. 6). beyond a general clarification of all parts seen in the previous figure. Optic and olfactory lobes have become more prominent, the myotomes more distinct and the tail is beginning to extend beyond the edge of the blastoderm. Stages similar to this, because they remain superficially unchanged for a relatively long period, are by far the most common in plankton samples.

The head with the rudiments of the visceral arches is becoming more differentiated by 26 hours (Plate 24. Fig. 7) while the tail is growing away from the yolk sac and curving slightly to the right (i.e., the left in the photograph since the embryo lies ventral side uppermost). The rudiment of the heart may be seen just below the olfactory lobe, curving forward from right to left in the figure A lateral view of a slightly later stage (30 hours) is shown in Plate 25, Fig. 7. The tail still has a blunt, rounded extremity. The heart shows as a slight projection on the ventral surface immediately behind the head, and begins to beat irregularly very soon after this stage. By 39 hours (Plate 24, Fig. 8) the tail has increased in length and has a more pointed tip than previously. The granular yellow pigment which is characteristic of the young larva is now plainly seen,

the heart beats fairly regularly, and occasional convulsive movements are seen in the embryo.

The embryo is ready to hatch at 45 hours (Plate 24, Fig. 9). The eyes, as yet lacking retinal pigment, have a clearly differentiated lens, while auditory capsules can be plainly seen on either side of the posterior extremity of the head, about 0.3 mm behind the centre of the eye. The tail is fully developed and terminates in a point. Yellow pigment spots are visible, particularly at the anterior and posterior edges of the eye and on either side of the tail (between 8 and 9 o'clock in the figure) though smaller spots occur at intervals along the body. This pigment, black in the photograph, is bright yellow by reflected light, and is probably one of the most useful diagnostic characters of the species at this stage. The heart beats regularly, and movements of the embryo within the egg membrane become more and more frequent toward hatching time Plate 25, Fig. 8 shows a lateral view of the same stage. Since the camera is focused on the more distant head region the photograph gives the illusion of reversing the caudal flexure. The embryonic median fin and myotomes in the tail may be seen clearly. An umbilicus near the right-hand side of the figure passes from the anal region of the embryo into the yolk sac.

Plate 24, Fig. 10, shows the same embryo commencing to hatch. This is accomplished by a periodic thrashing of the tail, which gradually distorts the egg membrane and eventually ruptures it, usually in the vicinity of the head From this point emergence may take place in a few minutes, though it is not unusual for up to an hour to elapse before the massive yolk sac is finally forced through the broken membrane and the larva escapes, leaving the empty egg shell behind as in Plate 24, Fig. 11. The tail flexure is retained for some time, often as long as 12 hours, and gives the larva a tendency to swim in circles. A lateral view of the same larva is shown in Plate 26, Fig. 1. Although, for the purposes of comparison, it is represented with dorsal side uppermost, the actual swimming position is normally inverted, and at rest the body lies at an angle of about 45 degrees to the horizontal, with the tail downward and the relatively buoyant yolk sac uppermost. It is only after about 24 hours that larvae eventually “right” themselves. Under laboratory conditions the newly-hatched snapper tend to float or swim in clusters near the surface of the water.

When viewed with the naked eye, the bright yellow granular surface pigmentation is characteristic. The three most prominent patches are on the head (particularly about the eyes), in front of the vent, and midway along the tail. This last patch may spread irregularly over several myotomes, but it is almost invariably centred on the 18th myotome behind the cephalic region. A further patch of variable size usually occurs immediately behind the head, while others still smaller are scattered along the dorsal surface and the ventral region behind the vent. Black or brown pigment is usually absent at this stage, but occasional melanophores, usually stellate in form may occur on the yolk sac or oil globule. The eye, still lacking retinal pigment, has all its principal components including a crystalline lens fully developed. The posterior extremity of the gut with a vestige of post-anal gut is plainly visible, while the mid-gut, though less obvious. may be seen from sections to have a distinct circular epithelial wall. The two-chambered heart may be seen beating regularly and lies obliquely across the ventral surface with the ventricle to the right. The auditory capsules are situated on either side of the hind-brain, where they appear as two transparent ovals, each

with a pair of dark spots near the centre. The median fin is continuous round the tail from the back of the head dorsally to the anus ventrally. Being thin and transparent, it is not always clearly visible by transmitted light, and is best seen when the illumination is slightly off centre. Fin rays are at this stage either obscure or absent.

After the first 24 hours (Plate 26. Fig. 2) the larvae usually prefer the bottom of the container, either resting head down, tail inclined at an angle of 45 degrees, or swimming in short bursts in the horizontal position as in the figure. The main characteristics seen at hatching are still present, but the body has increased in length from 2.1 to 2.7 mm, mainly by growth of the tail. At the same time the yolk sac has been reduced to about a quarter of its previous volume and is separated by about half its length from the anus. Yellow pigment has persisted but has become fibrous rather than granular, having an arborescent appearance where it lies on the surface of an organ such as the eye, the gut or the oil globule.

After two days (Plate 26. Fig. 3) the yolk sac is still more reduced in size and the body elongated to 3.2 mm. The rudiments of jaws have begun to form, though there is still no functional mouth. The alimentary canal is lengthening and becoming convoluted. Yellow pigment is still present, but is reduced in area, while small black melanophores are beginning to appear on various parts of the body. The retina of the eye is beginning to darken, but the lens is still distinctly visible. Small pectoral fins have commenced to develop.

After three to four days (Plate 26, Figs. 4 and 5) the larva appears to have reached the maximum development possible without external sources of food. Although there has been little gain in length (at least under laboratory conditions) considerable structural modification has taken place. The yolk sac has been completely absorbed, while the oil globule has disappeared. The jaws are completely developed and functional, and the gut has increased in size and become more convoluted. The retina is now pigmented a deep black, against which the lens can no longer be distinguished in side view, though from above it may be seen projecting into the space between retina and cornea. The pectoral fins are enlarged and fully functional and can be seen clearly from above. Yellow pigment has by now largely disappeared except for a few traces such as that on the tail in Figure 5. In its place black pigment has become more conspicuous as in the regularly spaced granules on the undersurface of the tail and arborescent patches on the surface of the gut and other organs. The median fin is still thin and transparent, but clearly developed fin rays may be readily distinguished.

Development ordinarily proceeds up to this stage in the absence of food, and in fact, for convenience of photography, several batches of larvae were raised entirely in filtered sea water. It has not as yet been possible to produce the environmental conditions necessary for development to proceed beyond this point. Obviously, suitable food is an essential, but the addition of plankton taken with a fine-meshed net in the vicinity of spawning grounds has so far not proved successful, perhaps partly owing to the fact that dead organic matter almost invariably accumulates in the container and is difficult to remove without undue disturbance of the larvae. Specimens have been kept alive for as long as 12 days from hatching, but beyond the fourth day development appears to be arrested and no significant changes in form are noted. Although food is an important factor in development at this stage, it is probable that other aspects