aperture, the mouth, placed upon the median, ventral line just behind the depressed ram-like termination of the body, and between it and the anterior portion of the abdominal cavity. This oral opening is of moderate size, and is surrounded by about thirty-one tentacles which are moderately long and slender, and bear upon their sides little protuberances which give them a toothed appearance. The anus, or outlet of the canal, is funnelshaped, and opens very eccentrically upon the left side of the body just beneath the level of the notochord and quite near the end of the tail. The left or free edge of this aperture does not extend at its posterior limits quite down to the ventral edge of the muscle-plates, so that the anus also opens, to a certain extent, towards the left side of the body, although the faces are expelled directly backwards and downwards along the side of the median fin. This free edge is quite flexible and in hardened specimens is so contracted, together with the surrounding parts, that the anal aperture appears to open into a pseudo-cloaca. The integument, which forms the greater part of the mouth tentacles, is thin and nearly transparent, and expands along the entire length of the dorsum, and around the tail, and as far forward as the branchiopore, into a delicate, median fin of nearly uniform width except upon the edges near the posterior extremity, where two unequal lobes are formed which represent the blades of this "lance" termination. Of these two "blades" the ventral is the larger, and its posterior curvature is nearly below the anal opening of the intestine. The integument also forms two longitudinal folds, which extend along either side of the abdomen, from the posterior portion of the mouth orifice where they originate, to the indentation which exists between the abdominal and the tail portions. Here, after forming a sort of triangular pit into which the branchiopore opens, they become merged into the median, ventral fin, which, as already stated, reaches forward to this point. When the abdomen is fully extended these folds become nearly obliterated, and are barely visible as lines running along the sides parallel to and at some distance above the ventral outline; but when the abdomen is strongly contracted they form prominent ridges along the lower edge of the body, and so change the appearance of the specimen that it is not much to be wondered at that Pallas should say, that this portion looked very much like the very narrow foot of a snail."

These folds are hollow and have been thought, until quite recently, to have an opening at either extremity, but Prof. Ray Lankester denies that there are any such openings, and I have failed to obtain any evidence from my specimens that any such apertures exist. With the exception of these side-folds and the mouth tentacles, the integument presents no appendages whatsoever. External sense-organs are also wanting, except upon the left side of the body near the anterior end of the chorda dorsalis, where a small ciliated pit is said to be located which it is claimed, by Kolliker, its discoverer, and others, represents a nasal depression, or cavity. I have not been able to make out this pit, and even if it is present, it is probable, that these animals gain their impressions of external objects entirely by the general sense of touch.

The adults, while varying somewhat in size, as is the case with most adult animals, do not differ very much otherwise in general appearance except during the breeding season, when the female becomes filled with ova, and the abdominal portion becomes, in consequence, much larger than ordinary. At this period the ova show very plainly as a row of large white spots along either side of the animal, Fig. 1, Pl. 1, but at other times, and in the males, there are no such spots visible to the naked eye. These differences of size and sexual appearance were well marked in my specimens, for while they varied in length from 1th to 17th inches, thus being of rather small size, the female, which was the largest, was so distended with ova that her body was much rounder, and consequently more opaque in appearance than the bodies of the thinner males. The young, Fig. 5, Pl. 1, and Fig. 7, Pl. II, resemble the adults very much in outline, but differ in many points of structure, which will be noticed in treating of their development, and in being quite transparent, looking much like animated bits of isinglass when in the water. This transparency, however, gradually gives place, as they grow old, to a semi-opaque condition which permits the outline of different parts to be made out, but not with any great degree of distinctness unless under a very strong light, and the older and larger the specimen, as a matter of course, the less the distinctness. The young specimens varied in length from 4th to th of an inch, although the greater number were about th of an inch long.

1On some new points in the structure of Amphioxus. Prof. E. Ray Lankester. Quar. Jour. of Micro. Science. Vol. 15, p. 257, 1875.

2 Müller's Arkiv, p. 32. Berlin, 1843.

All of the above-mentioned specimens which came into my possession, were gathered together during the period from the 9th of July, when the first specimen, an adult, was obtained, to the 2d or 3d of August, after which date no more could be found. The young were taken mostly at night, one or more at a time, when the water was comparatively quiet, but the greatest number captured on any one occasion was at noon of a very hot day, when there was scarcely a breath of wind, and the surface of the bay was almost as smooth as the proverbial "sheet of glass;" these small inhabitants thus seeming to be affected by heat, and especially by a quiet condition of the water, in very much such a manner as are the myriads of other young animals which are floated hither and thither by the currents of the sea at this season of the year. As soon as taken they were transferred to tumblers which had been previously filled with fresh sea-water, and each tumbler was generally occupied by four or five specimens. The water was changed daily in all the vessels. When first placed in these receptacles they darted about with a quick wiggling" motion which resembled somewhat the movement of a tadpole, but different in that the head, or anterior part of the body, moved from side to side as far and as vigorously as the tail portion. This peculiar undulation was generally kept up for some little time at or near the surface, when suddenly they would cease all motion and allow themselves to sink slowly to the bottom, where they would remain flat upon their sides until again impelled to action. When this impulse came, from whatever. cause, and they were once started from their resting place at the bottom, they generally swam directly upward to the surface, moved about here for a short time, and then, as before, suddenly stopped and allowed themselves to sink again to the bottom. But sometimes one of the inhabitants of a dish would start up, seemingly impelled by some willful freak, dash about close over the bottom and stir up all the others in the vessel, when there would be, for a moment or so, quite a brilliant display of undulating, flashing forms.

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The largest of these young specimens was pretty well advanced in development, and was placed in a separate dish which had a layer of sand upon the bottom. It was thus isolated for the purpose of ascertaining if it would make use of the sand as a place, of refuge, but only on one or two occasions, and then for very

brief periods, did it ever disappear beneath the surface. Generally it lay flat upon the top of the sand, until disturbed from its repose, when its actions closely resembled those of its smaller fellows. Hence it must be at a later period of life than that to which this one had attained, that these little animals cease to be shifted about by the flood and ebb of changing currents, and become "burrowers." The adults, which were taken from the banks by means of the dredge, were placed together in a large jar of sea-water, which was furnished, like the dish of the largest of the young animals, with a layer of sand upon the bottom. When once in the water they commenced swimming about very rapidly, with the same graceful, undulating motion which has been noticed as characteristic of the young, but with much greater vigor and elasticity. These movements were executed sometimes upon the back, sometimes upon the abdomen in the position of ordinary fishes, it seemed to make very little difference which side was uppermost, but I have never seen them move backwards, or tail-end foremost. After circumnavigating the vessel once or twice, gradually moving slower and slower, they would stop and sink down upon the sand at the bottom. Generally as soon as they touched the sand they would half-arch their bodies and almost instantaneously disappear from sight beneath the surface, thus regaining their natural place of refuge. After this disappearance they very rarely entirely emerged from their retreat, and as a rule, not at all during the day time. But if the surface of the sand was carefully examined at night, little spots might be detected where the sand appeared less compact than elsewhere, and a close inspection would discover each such spot to be a network of crossing tentacles arching over the expanded mouth cavity of one of these animals, which was thus, while lying belly upwards buried in the sand with only its mouth exposed at the surface, busily engaged in drawing its food from the water above.

Sometimes they could be found so situated during the day time, and now and then both by day and night, but rarely in the day time, one or more of them could be seen protruding part way from the sand, and looking as if planted in this position, but a tap or a motion of the vessel would cause them to withdraw from sight immediately.

These actions would seem to indicate what is probably a fact,

that the day time is to these animals a period of rest, when they remain entirely buried beneath the surface, and night time a period of activity, when they come up to feed and perhaps to move from place to place, as they have been seen swimming about during the night in the aquarium at the Zoological Station at Naples, and on one or two occasions I have found, early in the morning, one of my specimens lying entirely out of the sand, fully exposed to view, and in all probability it had been swimming about during the night.

On account of the propensity of these animals to remain concealed from sight it was necessary, whenever they were wanted for examination, to drive them from the sand, and this was by no means an easy task, as they are such exceedingly active little beasts that they would work their way from side to side of the dish beneath the sand, very nearly as quickly as I could run a stick or pencil through it in trying to find their position. And when once forced out, they would dart through the water so impetuously, and plunge into the sand again so quickly that their movement seemed merely a flash in the water, and a few particles of floating sand and mud would alone indicate that one of them had been out of their proper domain. Generally this chasing process had to be repeated four or five times, when they would become exhausted, and after undulating about the jar very slowly for a moment or so, they would sink upon the sand and remain perfectly quiet, flat upon their sides, for sometimes half a day at a time. During these intervals they could be transferred from dish to dish and even placed under a low power of the microscope for examination. But if not completely exhausted a short rest would revive them, and then, when touched, they would dash away as impetuously as ever, and I have had them, on such occasions, rush out of the water and over the broad rim of a large plate on to the table, and before they could be touched,. much less secured, throw themselves off the table and down upon the floor. But the adults appear to be so vigorous that these falls, which occurred on two different occasions, did not seem to have the least injurious effect. As may be surmised from this, all their movements are exceedingly quick, and this rapidity in going through sand and water, and hence the ease with which they can move about from place to place, is probably the reason why we secured only three of these animals at Fort Wool.

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