M0N0C4RAPH OF THE NORTH AMERICAN PKOCTOTRYPIDiE. 21 



is the formation of a proctoda-uui {(jli ) by an invagination, which ends Ijlindlj' in con- 

 tact witli the mesenteron. Shortly after this a thickening of the cpiblast {hsm) appears 

 along the ventral surface, which gives rise mainly to the ventral nerve cord ; this thick- 

 ening is continuous behind with the epiblast, which is invaginated to form the proc- 

 todicum, and in front is prolonged on each side into two procephalic lobes, in which 

 there are also thickenings of the epiblast (gsac), which become converted into supra- 

 CESophageal ganglia, and possibly other parts. 



Toward the close of the second larval jieriod the muscles {Jm) become segmentally 

 arranged, and give indications of the segmentation which becomes apparent in the 

 third larval period. The third and last larval stage (Fig. 2, E) oi Platijgasier, dur- 

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

 tures. The passage from the second to the third form is accompanied by an ecdysis. 



TKE LARV.E; TlfEIR HABITS AND PUPATION. 



The larv?e are all, apparently, internal feeders, apodous and with 

 minute mandibles. Those living in eggs transform into pupa3 within 

 the empty egg-shell of their hosts; sometimes a half dozen or more 

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

 — Scelio, Macroteleia, etc. — only a single specimen is found in each egg. 

 Those species that affect the larva? or i)upae of other insects either 

 gnaw their way out and spin small silken cocoons {Ccphalonomia 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 

 host {Platygaster and others). 



Lygocerun and alii ed genera, living in the Aphidida^, gnaw a hole 

 throagh 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 their host, which, in lieu 

 of a cocoon, affords ample protection for the larvie 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 fi'e- 

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



DISTRIBUTION. 



The Proctotrypidtie are apparently widely distributed over the whole 

 world, although oiitside 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 jjredict the species will be found 

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

 the Chalcididaj; judging from my own collecting I should &3>y 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 



