20 



BULLETIN 45, UNITED .STATES NATIONAL MUSEUM. 



appearauco in the caudal region, and divide tlii« part of the embryo into Kucccssive 

 segmeuts. AVhile these chauges have been taking jihico in the general form of the 

 embryo, the epiblast has given rise to a cutiele, and tlie hypoblastic cclLs have be- 

 come dilferentiated into a central hypoblastic axis — the uieseuterou — and a snrronnd- 

 ing layer of jnesoblast, some of the cells of which form hmgitudinal mnscles. 



With this stage closes wliat may be regarded as the embryonic development of 

 platygaster. The embryo becomes free from the amnion, and presents itself as a 

 larva, which from its very remarkable characters lias been spoken of as the Cyclops 

 larva by Ganiu. 



Tlie larviB of three species liave been described by Ganin, wliich are represented 

 in Fig. 2, A, B, C. These larva', are strangely dissimilar to the ordinary hexapod 



FlQ. 2. — Einliryoiiic hirval (Icvclopniciit of plntygaster: A, 15, C, ('y'lup^ larv;i' of t'nc isiiccics of 

 platygaster; ]), st'cond larval stage; E, third larval stage; '>iw, luoutli ; a, aiiteiuja; If, lioDked 

 feet; e/g, lateral feet; /, brandies of tail; vl, lower lip; sllcf, oesophagus; (;sac, supra-(>so])liageal 

 ganglion; bsm. ventral ei)il)lastic plate; Ivi, lateral musrles (tbe letters also point in D to tlie sali- 

 vary glands) ; <//(, proctodauni ; fia, generative organs ; in <?, mandibles; nf/, duets of salivary glands; 

 sp, (in E) salivary glands; lulx, stomaeh; cd, intestine; ei"^ rectum; ao, anus; tr, traclie;!'; //.■, fat 

 body. (After Ganin.) 



type, whether larval or adult. Tbey are formed of a eepbalotli<>raei<' sliield witli 

 the three pairs of ai)i)endages («, If, lj'<j), the development of wliieh has already 

 been described, and of an abdomen formed of live segmeuts, the last of which bears 

 the somewhat varying caudal appendages. The nervous system is as yet undevel- 

 oped. The larvae nu)vo about in the tissues of their hosts by means of their claws. 



The first larval condition is succeeded by a second with very different characters, 

 and the passage from the first to the sccoud is accompanied by an eedysis. 



The eedysis eonunenees at the caudal extremity, and the whole of the last segment is 

 comjdetely thrown olY. As the eedysis extends forwards the tail loses its segmentation 

 and becomes strongly com]>re88ed, the a]>pendages of the cejihalothorax are thrown 

 oft' and the whole embryo assumes an oval form without any sharp distinction into dif- 

 ferent regions and withojit tbe slightest indication of segmentation (Fig. 2, 11). Of 

 the internal chauges w-hich take jdace during the shedding of the cuticle, the lirst 



