SIPHON APTERA AND DIPT ERA 



377 



writers confused the amniotic cavity with the proctodaeum, giving rise to 

 erroneous interpretations. As development continues, the caudal end 

 pushes still farther forward ; the proctodaeum deepens ; and from near its 

 extremity, dorsal and ventral diverticula, the beginnings of the Mal- 

 pighian tubules, appear. The posterior mesenteron rudiment is closely 

 fused with the apex of the proctodaeum. At this time the head and tail 

 end of the embryo lie rather close together, a condition that, however, 

 does not last long (Fig. 331^). Then the shortening of the embryo 



proct 



Fig. 332. — Calliphora erythrocephala. Sagittal sections of two stages, A and B. (ect) 

 Ectoderm, (ent) Entoderm, (ggl) Nerve ganglion, (malp) Rudiment of Malpighian 

 tubule, {mes) Mesoderm, {proct) Proctodaeum. (stom) Stomodaeum. (y) Yolk. 



begins and continues until the anal end again lies at the posterior end of 

 the egg (Figs. 332^, B). 



When the germ band has reached its greatest length, the transverse 

 amniotic invagination marks the caudal extremity as seen from the dorsal 

 surface (Fig. 333). At this time the vestiges of six pairs of stigmatal 

 ectodermic invaginations are also in evidence, the first stigmata appar- 

 ently belonging to the mesothorax. Anteriorly in dorsal aspect the two 

 head lobes are visible. At this stage distinct segmentation may be seen 

 on the ventral side. 



The salivary glands according to Graber (1889) first show as paired 

 ectodermal invaginations between the third and fourth head segments or 



