By the forty-fifth day more new segments had evidently been developed by the germinal membrane, soon to be exposed by another change of skin that was about to take place. The Julus ceased to eat, became torpid, and lay coiled up in a spiral form. The tegument of the body began to assume a whitish crustaceous appearance, and the ani mals secreted themselves beneath any dry co vering, but avoided parts too wet. The princi pal changes in their general appearance were in the eyes, each ocellus being much more dis tinct, and in the germinal space, which was developed to its greatest extent, and distinctly exhibited the six new segments.
The change of skin, according to Mr. New port, is effected in the following manner. The young Julus, when about to cast its integu ment, bends its body in a semicircular form, with its head inflected against the under sur face of the second segment. In this condition it remains for several hours with its legs widely separated and the dorsal surface of the segments extended. The head is then more forcibly bent on the sternum, and a longitudinal fissure takes place in the middle of the epicranium, and is immediately extended outwards on each side posteriorly to the antennae in the course of other sutures, the analogues of which Mr. Newport has described as the triangular and epicranial sutures. Through the opening thus formed in its covering the head is then carefully withdrawn, and with it the antennae and parts of the mouth, and afterwards the anterior seg ments and single pairs of legs. The first and apparently the most difficult part of the shed ding of the skin is its detachment from the posterior segments of the body and from the interior of the colon. To effect this the ani mal, which has been previously lying coiled up in a circular form, first straightens its whole body ; it then forcibly contracts and shortens itself, especially at the posterior part, and by this means becomes greatly enlarged in bulk at its middle portion, but smaller at its extre mities. During these efforts, which are some of the most powerful it is able to make, the skin becomes loosened from its posterior parts, and while still contracting its segments, the anal extremity, and with it the entire lining of the colon, become completely detached, and from these it gently withdraws itself within the old skin in which the body is encased as from the finger of a glove. This is precisely what takes place in the shifting of the skin in insects. Having effected this part of its labour all the posterior segments are again shortened ; the animal once more disposes itself in a circular form, and after repeated exertions succeeds in bursting the tegument of the head in the part just described. As in the case of true insects
the young Julus entirely empties the alimentary canal by voiding its faces and ceasing to eat for one or two days preparatory to undergoing each transformation. When examined imme diately before the change there are no other symptoms of new legs than slight elevations of the skin, and this perhaps accounts for the length of time occupied in the change, the new legs requiring time for further developement before the old skin is thrown off.
Having cast its skin and thus attained the fifth period of developement, the young ins (fig. 325) has three elli on each side of the head, seven joints to the antennae, thirty-four legs, and twenty-one segments to its body. On the forty-eighth day this has been accomplished, and the young Ju his exhibits a marked alteration in its ap pearance. The an tenna; are considerably longer than the head, with seven distinct joints, and, as in the adult, the apical one is short and inserted into the sixth. The single eye has disappeared, and in its stead three distinct ocelli, arranged in a triangle, have been developed. The new segments of the body produced at the former change of the animal, from the eighth to the twelfth in clusive, (8-120 are now of the same size as the original ones, and each has developed from it two additional pairs of legs so that the whole number of legs is now thirty-four. The thirteenth, or, if we may so name it, germinal segment Of the last period, is less de veloped than the preceding ones, and is distin guished from them by the circumstances that it is smaller, possesses no legs, and has no lateral spot which exists on each of the preceding seg ments to the seventh, marking the existence of the foramina repugnatoria. The germinal space (13-19) which existed in the preceding period and was then seen to be forming seg ments, is now developed into six new apodal segments, from the 14th to the 19th inclusive, very much smaller and shorter than the rest, and a germinal space (h) is again forming be tween the last of these and the penultimate segment of the body, which, as above stated, undergoes no marked change. The whole body is thus composed of twenty-one segments, including the head. The first twelve of these are now perfectly developed, as well as the last two, the intermediate ones being only in their preparatory states. The animals at this period ate voraciously some decayed leaves, rotten elm-bark, and raw potato.