BIONOMICS AND DEVELOPMENT OF LYGOCERUS sp. 121 
proved impossible to keep one larva alive for observation from 
day to day. The reasons for determining the different instars 
thus are as follows : 
The newly hatched (first instar) larva of Lygocerus 
possesses only two pairs of open spiracles, but examples twelve 
hours old have four. At one time I believed that these forms were 
separated by a moult, though it was never observed. On the 
other hand, I noticed a larva twenty-four hours old which had 
the cast skin attached to the hind part of the body. The 
exuviae were too much torn to show the spiracles, but the larva 
itself had four (fig. 4). For purposes of convenience, there- 
fore, I have referred all stages up to that represented in that 
figure to first instar, and assumed that the spiracles of the third 
and fifth segments opened as the stadium proceeded ; but it 
may well be that there is a moult between the forms with two 
and those with four spiracles. We should then have five 
larval stages, separated by four moults. 
Similarly, the actual ecdysis between instars two and three, as 
here described, has never been observed, but the differences in 
the external form and respiratory system seem sufficient to 
place them in separate instars. 
The difference in size and form between instars three and four 
is so great that, if a large number of larvae had not been 
examined, there would have been doubt in referring them to the 
same species. The fourth instar, immediately after the moult, is 
transparent, and half the size of that represented in fig. 7. But 
the caudal appendage and tracheal system are unmistakable, so 
that although the actual eedysis has not been seen, this form has 
been described as the fourth instar. 
PUPATION AND EMERGENCE. 
The period of pupation is from fourteen to sixteen days. If 
disturbed, the pupa jerks its abdomen vigorously from side to 
side. It is possible that this habit, which is marked in both 
the larva and the pupa, and in which they differ from the 
Aphidius itself, and from its Chaleid and Cynipid parasites. 
