EXTERNAL ANATOMY OF INSECTS. 47 
oO 
which is peculiar to the Hymenoptera, Diptera, and one 
tribe of the Neuroptera, as the representative of the pro- 
thoraz in the other Orders, and this opinion seems, at this 
time very generally adopted, but subsequent observa- 
tions have caused me to entertain considerable doubts 
of its correctness. Many other Entomologists have 
thought it improper to distinguish these parts by the 
same name*. Much, however, may be said on both 
sides of this question, and I shall now lay before you the 
principal arguments that may be adduced in defence of 
each opinion, beginning with those that seem to prove 
that the collar zs the analogue of the prothorar. First, 
then, the collar, like the prothoraz, is placed precisely 
over the antepectus, and being placed in the same situa- 
tion, on that account seems entitled to the same denomina- 
tion ; especially as in some genera, for instance Chlorzon, 
it assumes the very semblance and magnitude of a thoracic 
shield, and is separated from the mesothorax by a con- 
siderable incisure. Again, in some cases that have fallen 
under my own observation, the collar is endued with 
some degree of motion distinct from that of the alitrunk, 
since in Pompilus and Chrysis the animal can make the 
former slide over the latter in a small degree. A third 
and last argument is, that no prophragm is formed 
from the collar: insects that have a thoracic shield are 
generally distinguished by having the anterior margin 
of the dor'solum deflexed so as to form a septum, called in 
the table the prophragm, which enters the chest and se- 
parates the cavity of the mesothorax from that of the pro- 
thorax ; now in Hymenoptera this septum is a process 
@ Latreille Organisation &c., 199. Chabrier Sur le Vol des Ins. 
c. 1. 412. c. iv. 54. &e. 
2N 2 
