AND THE DEVELOPMENT OF 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 Iulidse, 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 more 
distinct ; and in the germinal space (g), which was now developed to its greatest 
extent, and distinctly exhibited the six new segments. 
The casting off the shin, 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withdrawn, and afterwards the anterior segments, and then the rest of the body.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 antennse, 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 antennse and part of the mouth, and afterwards the anterior seg- 
ments and single pairs of legs. The first, and apparently the most difficult part of 
the shedding of the skin by lulus , is its detachment from the posterior segments of the 
s 2 
