282 



EMBRYOLOGY OF INSECTS AND MYRIAPODS 



into the embryo until their inner ends touch each other. After blasto- 

 kinesis, the embryo rapidly approaches the definitive nymphal type. 

 The embryonic envelopes become enclosed in the mesenteron, whereupon 

 the closure of the dorsal wall is completed. The pleuropodia then 

 extend their cell tips to enclose the embryo in a cytoplasmic sheath 

 which Hagan has termed the " pleuropodial extensions" (Fig. 214, 

 pleur. e); the enclosed space he terms the " pleuropodial cavity" {pleur. c). 

 From the initiation of blastokinesis until the completion of the pleuro- 

 podial extensions the embryo lies free in the maternal reproductive tract 

 p2 ".eurp 



Sin 



Fig. 214,^Hesperoctenes. Cross section after blastokinesis. {ant) Antenna. {ect) 

 Ectoderm, iggl) Ganglion, (mes) Mesoderm, {neurp) Neuropile, (oen) Oenocytes. 

 (p) Thoracic legs, (pleur) Pleuropodium. (pleur. c) Pleuropodial cavity. (pleur. e) 

 Pleuropodial extension, (sin) Haemocoele. (trc) Trophocyte. (tro) Mouth parts. 

 (From Hagan.) 



without attachment to the mother and without protective covering, an 

 unusual condition. 



The nutritive function is performed by several structures. The fat- 

 like substance that accumulates in the egg comes from the epithelium of 

 the tubule. The nurse-cell body seems to be derived from the follicular 

 epithelium, the usual source of the egg follicle. The serosa develops from 

 the blastoderm and, functioning as a trophserosa, absorbs the nurse-cell 

 nutrients. The trophocytes (vitellophags) elaborate in succession the 

 substances available to them within the serosa, the pleuropodial cavity, 

 and the mesenteron. Finally, the pleuropodia take over this function 

 and continue to supply the embryo with nutriment until shortly before its 

 extrusion from the mother. In so doing they function in a manner 



