NEVROPTERA AND COLEOPTERA 



301 



the egg. As the tail grows toward the anterior pole, it has a tendency to 

 return to the middorsal line. In the meantime the head has grown along 

 the ventral side of the egg until when the embryo reaches its greatest 

 length, the head and tail are close together at the anterior pole (Fig. 252). 

 While the embryo increases in length, the amnion grows laterally 

 between the yolk and the serosa until the folds from the caudal half of the 

 embryo meet and fuse with those from the anterior half, enclosing the 

 embryo everywhere within two membranes. The last point of fusion is 

 near the tail where the inner portion of the amnion joining the head and 

 tail remains connected with the outer amniotic envelope by a thin strand 









■ism 







v-'f 



J-. • 



Fig. 243. — Brachyrhinus. Third- 

 day embryo. Head and first two 

 thoracic segments. 



Fig. 244. — Brachyrhinus. Third- 

 day embryo. Second and third 

 thoracic segments and abdomen. 



of amniotic tissue. The amnion and serosa remain intact until the larva 

 cuts through them in the process of hatching. 



After blastokinesis, when the tail has reached the surface and the 

 embryo has straightened out, segmentation begins, becoming evident 

 when the embryo reaches its greatest length. Figures 243 and 244 

 represent an embryo three days old showing the gastrular groove com- 

 plete from the stomodaeum to the proctodaeum with segmental grooves 

 plainly showing for slightly more than half the length of the germ band. 

 The gnathal appendages, as yet consisting of simple lobes only, are 

 present, as is also a single pair on the first thoracic segment. Antennae 

 are also visible, but there is no differentiation between antennae, mouth 

 parts, or the single pair of thoracic lobes. The labrum appears as a simple 

 flap above the mouth opening. Paterson reports that two lobes appc^ar 



