410 EMBRYOLOGY OF INSECTS AND MYRIAPODS 



the molt at the beginning of the second postembryonic developmental 

 period. Consequently the two pairs of ganglia by the constriction of 

 the necks of the depression lose their connection with the ectoderm of 

 the future body wall. The nerve connection between antennae and 

 deutocerebrum is early established. Pflugf elder (1932) states that he 

 made no observations on the origin of the tritocerebrum, a part that is 

 poorly developed in the Myriapoda generally. The ganglia of the 

 ventral nerve cord arise in the same manner as the brain lobes with the 

 formation of cup-like invaginations of the ectoderm which are later cut 

 off from the surface. Of these there is a pair for the antennal, mandib- 

 ular, maxillary, and postmaxillary 

 "■■"•••••.... segments and two pairs for each 



\ of the following segments. 



Blastokinesis, or flexure of the 

 embryo during development, oc- 

 curs by the folding in of the 

 embryo into the yolk, the bend 

 occurring at about the second 

 maxillary segment leaving only 

 clypeus and telson exposed at the 

 surface (Fig. 368). 

 * . . j~ With blastokinesis modifica- 



tions in certain structures are me- 



FiG. 368.— Plat urhacus amauros. Germ , . ,, i ux i_ i. rr^i. 



band in surface view after flexure, {ant) chanically brought abOUt. the 



Antenna, (cly) Clypeus. (tel) Telson. postmaxiUarV segment (second 



(From Pflugf elder.) ."^ ,, , 



maxillary) is relatively small, and 

 earlier writers maintained that the appendages were lacking. Pflugf elder 

 has shown that the appendages, though small, are present. They are 

 closer together than the appendages of the maxillae so that when blasto- 

 kinesis takes place the former are pushed between the latter, where they 

 later fuse into a single structure, the gnathochilarium. The sternite of 

 the second maxillary segment forms the gula (hypostoma of Latzel) ; the 

 tergite forms the collum, which accordingly is a part of the head although 

 not fused with the preceding parts. 



Before the rupture of the chorion the embryo molts, although the 

 skin still remains around it. This molt may be regarded as the beginning 

 of the postembryonic period, since it is accompanied by an increase in 

 the number of abdominal appendages, despite the fact that the chorion 

 has not yet been shed. 



Julus terrestris Leach 



Heathcote (1886) states that in Julus terrestris the yolk forms early 

 into yolk spherules which are present up to a very late stage of develop- 



