MONOORAPH OF THE NUUTII AMICKICAN PKOCTOTUYIMD.E. 21 



is tho forniiitioii of u proctod.i'iini i.'/'O ••> a'» invii^iiiatiim. which eiuls Mindl}- incou. 

 tilctwitlitheinosonteroii. Short ly after this a tliiikfiiinj; of thoopibhitit^^*"!) ajipears 

 ah)iij? tho ventral surface, which jjives rise iitainly to the ventral uervecord ; thiH thick- 

 oiiiiiK is continuous behind with thoepiblast, which is inva<;inated to form tho proc- 

 toda-uni, and in front is prohnigcl on each side into two jtrocephalic lobes, in which 

 there are also thickonin'48 of tlie <'piblast ((jmc), whicdi become converted into supra- 

 a-sopliaf^eiil j^anglia, and jtossibly other i>arts. 



Toward the close of the second larval period the muscles (/m) become segnientally 

 arranged, and {ji^'" iudications of tho segmentation whic'.i becomes apparent in tho 

 third larval period. Tho third and last larval stage (Fi^:. 2, K) of I'latytjoBter, (hir- 

 ing which it still remains in the tissues of its host, presents no very peculiar fea- 

 tures. The passage from tho secoml to the third form is accomnanicd by au ecdyaia. 



The larviB are all, apparently, internal feeders, apodous and with 

 minute mandibles. Those living in eggs transform into pupie within 

 the empty egg shel) of their hosts; sometimes a half dozen ov more 

 being found within a single egg-shell, although of the larger scelionids 

 — Scelio, Maeroteleia, ete. — only a single specimen is foun<l in each egg. 

 Those species that affect the larvje or pupae of other insects either 

 gnaw their way out and si)in small silken cocoons (('rphalutiomia and 

 other bethylids), or else weave silky or parchment-like cocoons, often 

 arranged in parallel rows, side by side, within the empty skin of their 

 hoat {Platygaster and others). 



i>y</ocerj<s and allied genera, living in the Ai>hidi(Ue, gnaw a hole 

 thiough the ventral surface of the aphis, and after securely fastening 

 the aphid by a silk -like secretion to the leaf or twig upon which it 

 has been feeding, pupate within the body of tlieir host, which, in lieu 

 of a cocoon, affords ample protection for the larvae to undergo their 

 transformations. I know of no proctotrypid that transforms loosely 

 into a pupa without a covering or protection of some kind, as is fre- 

 quently, if not invariably, the case amongst the Chalcididae. 



DISTRIBUTION. 



The Proctotrypidie are apparently widely distributed over the whole 

 world, although outside of Europe little is as yet known of the exotic 

 forms, and it is not possible, therefore, to generalize upon the genera 

 and their distribution. From an examination of various exotic col- 

 lections of Hymenoptera, it is safe to predict the species will be found 

 to be numerous and widely distributed, but far less numerous than 

 the Chalcididfe; judging from my own collecting I should say less 

 than one-fiftieth in number. Only a very small percentage of the 

 species is yet described. 



Our species, except in a few cases, fit very well into the established 

 European genera; but from South America it was found necessary to 

 erect many new genera, and doubtless this will be found to be neces- 

 sary with collections brought from other regions. Very few species 



