In about an hour after leaving the amnion the young Julus exhibited a marked change. Its head was elongated on the prothorax (2), the parts of the mouth were distinctly move able, and the eye, a single ocellus on each side of the head, acquired a darker colour. The whole body had been increased at least one fourth in hulk since leaving the amnion. It now measured about a line in length, and ex hibited very distinctly the nine original seg ments The seven anterior of these were strongly marked. In the germinal space, (fig. 321, JD between the original seventh and eighth segments, six new segments were now developed. These were still very small, the length of the whole being equal only to that of one of the original segments. At the present time they did not form independent divisions of the body, but were covered by the common tegument, and thus appeared like supplementary parts of the seventh segment produced from the germinal membrane and interposed between the seventh and the penultimate segment (8), which, as be fore stated, is a permanent segment throughout the life of the animal. This latter fact shows that it is not merely by an elongation and division of the terminal segment that the body of the Julus is developed, but that it arrives at its per fect state by an actual production of entirely new segments; that these are new growths or formations which are in progress long before they are apparent to the eye, and that the original segments of' the ovum into which the animal is first moulded are permanent segments throughout its whole life.
But still more curious is it that not only have new segments been formed as described, but that the common tegument by which they are now covered and which also invests the whole body as the tree skin, has already begun to be detached preparatory to its being thrown off, as is shewn in the fact that the new segments are now seen beneath it ; and it is further remark able that this deciduation of the first skin of the animal had actually commenced before the bursting of the amnion. These circumstances explain the cause of the very quiescent state of the young Julus, and its almost and perhaps entire abstinence from food whilst this skin remains on its body. It is not until this skin is thrown off that the new segments become elongated, and the Julus then appears suddenly to have acquired six new divisions to its body.
The production of new legs is equally cu rious. Up to the present period the animal has but six legs (fig. 322, b a), but four addi tional pairs are nevertheless in the course of formation. These at present exist only as eight minute nipple-shaped prominences on the under surface of the sixth and seventh segments (b four on each, covered by the common tegu ment, which, we have seen, is becoming deci duous. The three single pairs of legs that now exist as the only locomotive organs are attached, one pair to the prothorax or second segment, one to the third and one to the fifth segment. The fourth, or segment intermediate between these last, never possesses any legs, but in the female contains the outlets of the organs of ge neration. The general appearance of the ani mal has now become less delicate, the head has acquired a darker colour, and a faint broad patch (fig. 322, p) is now making its appear
ance at the anterior part of the seventh seg ment. This patch, which is permanent through all the ear lier changes of the animal, is of the greatest utility in de termining the pro duction of new seg ments. It is in the segment imme diately posterior to this that the male organs find their ou t let, a circumstance the more remarkable from the fact that this outlet is in the anterior part of the original germinal space, and at the bursting of the egg this is very near the termination of the body. Such was the condition of the young Julus one hour after leaving the amnion. It soon began to exhibit its animal powers, to sliew the instincts peculiar to its species, and to be sensibly affected by ex ternal causes. In less than six hours from the bursting of the amnion the little creatures were in motion. At first the antennae were the or gans employed. They were moved slowly to and fro, and seemed to gain power by use. In a short time the limbs began to be extended, and the animal slowly raised itself upon them for the first time. Its first efforts at locomotion were exceedingly feeble, but it gradually gained strength. At the end of twelve hours the em bryos crawled slowly about, but moving the an tennae briskly. On exposing them to a strong light a marked effect was produced in their movements. They evidently were greatly af fected by it, and seemed instinctively to shun it. This was the first marked exhibition of instinct. Locomotion was at first performed very slowly but with instinctive care. The anal segment, previously to each step, was expanded like the anal leg of the larva of an insect, and being first attached like a true pro leg, and its step, as it were, measured, its body was carried forwards by a?, effort that extended, as in insects, from segment to segment.
At twenty-four hours after escaping from the amnion the young animals were lying toge ther in a heap, but when disturbed seemed to have acquired more power of moving : they remained quiet except when aroused, and had not yet taken food. The only marked diffe rence in their appearance, excepting that they had still further increased in size, was in the nipple-shaped protuberances on the sixth and seventh segments, the rudiments of future legs. These were now more distinct and mammiforin. Ten hours later in the day they assumed still more the appearance of nipples projecting from the under surface of the segments. When examined in specimens that had been placed in spirits of wine, it became evident that these projections were occasioned by the develope ment under the deciduous tegument of four new, but exceedingly minute legs, complete in all their parts, each covered by its proper skin. The claws to the legs of the other segments were also more strongly marked. The new segments (f) were more developed, although still covered by the common tegument, and, as in the preceding state, forming only one divi sion of the body, while a small space behind them indicated the point from which other new segments were to be produced.