AND THE DEVELOPMENT OP THE MYRIAPODA. 125 



entering their fifth period when others have not yet passed their fourth. This I have 

 no doubt was the case with these lulidse, some of which acquired their two addi- 

 tional pairs of legs on the thirty-first day, others on the thirty-second, and some not 

 until the thirty-fifth, and thirty-sixth and seventh ; while the remainder did not un- 

 dergo this change at all, but continued to feed and remain active, and instead of now 

 acquiring two pairs of legs, acquired ten pairs at their next change, or fifth period of 

 development. 



On the forty-fifth day (fig. 20.) the whole of the remaining specimens were prepa- 

 ring to undergo their transformation. This appears to have been their proper period 

 of change. The variation in the shedding of the skin just noticed, includes, from the 

 time when the first specimen changed, to the completion of that process by the last, 

 a period of six days. The specimens had now acquired a much darker colour, and 

 the marking on the seventh segment was becoming paler. This was one day before 

 the change. The temperature of the room was now 65° Fahr. What renders it more 

 probable that the preceding was a pseudo-change, is, that I was unable to rear any 

 of the specimens which underwent it, while others that attempted to change a little 

 subsequently to those at the period noticed, perished in the attempt. The proper 

 period was now approaching. On the forty-fourth day the specimens had ceased to 

 take food, seemed torpid, and lay coiled up in a spiral form ; the tegument of the 

 body now began to assume a whitish crustaceous appearance, and the animals se- 

 creted themselves beneath any dry covering, but avoided parts too wet. The principal 

 changes in their general appearance were in the eyes, each ocellus being much moi*e 

 distinct ; and in the germinal space (^), which was now developed to its greatest 

 extent, and distinctly exhibited the six new segments. 



The casting off the skin, as in insects, is a tedious and eventful occurrence to the 

 young lulus. Waga states that the skin of the lulus bursts on the under surface of 

 the body in the thoracic region, between the single pairs of legs ; that the head is first 

 withdrawn, and afterwards the anterior segments, and then the rest of the body. I have 

 been unable to confirm his account as to the part at which the skin is fissured. 

 According to my own observations, when the young lulus is about to change its skin, 

 it bends its body in a semicircular form, with its head inflected against the under 

 surface 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 I have elsewhere described in insects as the triangular and epicranial sutures. 

 Through the opening thus formed in its covering the head is first carefully withdrawn, 

 and with it the antennae and part of the mouth, and afterwards the anterior seg- 

 ments and single pairs of legs. The first, and apparently the most diflScult part of 

 the shedding of the skin by Julus, is its detachment from the posterior segments of the 



s2 



