20 



Un-LpniX 15, UNITKU STATKS NATIONAL Ml'SKlIM. 



nppearaiH'(i in tlio i-aiuliil n-gion, mid divide lliiH )>art of tliii iMiibryu into HiicrcMtivo 

 seguieuts. W'liih? tli<so rliaii;itn liavci hi-oii taking i)la<'t< in tlio general fonnoftho 

 cinbrjo, tlu) j'liildast liaH given lino to a (iitirle, and tin) liyptiblaslic cells liave, lie- 

 come difl'erentiated into a central hypobliiHtic axis — tln^ntwenteron — an«l jVHnrronud- 

 ing layer of niesoldast. Monie of the cells of wliich form longitudinal ninscles. 



With tills stage closes what maybe regarded as tho »'niliryonie dev<;lo|)ment of 

 jdatygastcr. Tho embryo bcM-omcs free frc»m the amnion, and jiresentM itself as a 

 larva. \vlii< b from its very remarkable characters has been spoken of as the Cyclops 

 larva by <ianin. 



Tlie larva) of three sjieiies have ))een described by (ianin, which are represented 

 in Fig. 2, A, 15, ('. These larva- are strangely dissimilar to the ordinary bexapod 



Fig. 2. — Eiiihryouio larval <l('velopni('iit of plntyg.istcr : A, T?, C, Cyrlojts larvie of t'ri'o spec its of 

 platygasttT; D, sccoiid larval stago; K, tliinl larval sta^c; jho, iiiontli; a, antoiiiia; kf, liookcil 

 feet; efri. lateral f.ct; /, liraiulics of tail; iil, lower lip; «?A/, n'soi>ha;;iis : i.nai', .siii)ra-(rno|iliageal 

 ganglion; bsiit. voiitr;;] ciiililastic plate; Im, lateral iiniseles (the letters also jmint in D to tlie Hali- 

 vary glands) ; (/^, ]»roeto»l;einn ; r/n, generative organs; J/i</, iiiauilibles; a<j, (liietsof salivary glands; 

 f^\ On E) salivary glands; Ml*, stoinaeh ; ed, intestine; <•«•, rectum; ao, anus; tr, trache.v; fk, fat 

 bodj'. (Aftertianin.) 



typo, whether liirval or adtilt. They are formed of a cepliabtthoracie shield with 

 the three pairs of iippendages (a, If, Ifij), tho development of which has iilroady 

 been described, iind of an abdomen formed of iive segments, tho last of which bears 

 the somewhat varying caudal tippendiigcs. The nervous system is as yet tiudevel- 

 oped. The larva) move about in the tissues of their hosts by means of their claws. 



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

 and the i^assage from the first to the second is accompanied by an ecdj'sis. 



The ecdysis coinmeuces at tho ciindal extremity, and the whole of the last segment is 

 completely thrown off. As tho ecdysis extends forwards tho tail loses its segmeutatiou 

 and becomes strongly compressed, the ajtpendages of tho ccphsilothorax ii.ro thrown 

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

 ferent regions and without the slightest indication of segmentation (Fig. 2, 1>). Of 

 the internal changes which take place during the shedding of the cuticle, the first 



