HETEROMORPHA. 



365 



rounded embryonic rudiment, in which an outer ectodermal layer and an inner 

 (lower) layer can soon be distinguished. The embryo now lengthens and is soon 

 divided by means of a groove which sinks in ventrally into an anterior widened 

 cephalic section and a posterior narrowed section. The stomodaeum appears as 

 an ectodermal invagination in the cephalic section, and soon becomes connected 

 with the enteron which has developed from the inner cells. The proctodaeum 

 arises considerably later, and does not communicate with the enteron until a 

 very late stage. In the cephalic section (Fig. 182) a pair of grasping hooks (kf) 

 develop at the sides of the mouth, and behind these a lower lip [ill). Another 



Fig. 1S2. — Stages in the development of Platygaster (after Ganin, from Lubbock). 23, 2h, 25, 

 so-called Ctyctops-like larvae of three species of Platygaster ; 26, second larval stage ; 27, third 

 larval stage, a, antenna ; ag, salivary duct ; ao, anus ; bsm, ventral ectodermal thickening ; 

 ed, intestine ; ew, rectum ; /, furcal appendage ; fk, fat-body ; ga, genital organs ; gh, 

 proctodaeum ; gsae, supra-oesophageal ganglion ; kf, hook-like feet ; Ifg, lateral limbs ; 

 tin, sp, salivary glands; md, mandibles; mo, mouth ; ms7, stomach; dk, slkf, oesophagus; 

 tr, tracheae ; id, lower lip. 



pair of limbs {Ifg) arise later at the posterior boundary of the anterior section, 

 and a pair of short antennae (a) develop anteriorly. The posterior section of 

 the embryo becomes divided up into several segments and runs out into a fork- 

 shaped appendage (/) recalling the furca of the Copepoda. On this account the 

 first larval stage that hatched from the embryonic integument after the harden- 

 ing of the chitinous cuticle, was known as the Cyclops-like stage (Figs. 182 and 

 183). It appears that, in this stage, only the intestinal canal and the limb- 

 muscles have been differentiated, while the other still undifferentiated organs 



