APPEARANCE OF THE BODY-SEGMENTS 



537 



and flaring flaps, which are called the procephalic lobes. It 

 becomes the antennal segment. 



P 



.tti. 



FIG. 513. Two stages in the spreading of the indusium. A, lateral view of egg just after the 

 arrival of the embryo on the dorsal yolk. B, lateral view of the egg with the indusium nearly 

 reaching the poles. C, same egg seen from the dorsal surface. 



The mouth (stomodveitm) now develops, and is situated at the 

 anterior, 1 and the rectum (proctodmum) at the posterior pole, or end 

 of the primitive band. 



In Blatta, Hydrophilus, the Trichop- 

 tera, and the Lepidoptera the hindermost 

 part of the primitive band is turned in 

 ventrally (Figs. 534, C). 



The preceding account of the relations of the 

 primitive band to the yolk does not apply to all 

 insects, since there are variations which appear 

 to depend on the form of the egg, and on the 

 amount and distribution of the yolk-masses. In 

 certain Coleoptera, the primitive band sinks down 

 and thus becomes immersed into the yolk. In 

 Donacia (Kolliker and Melnikow) and Hydro- 

 philus (Heider), and in the Chrysomelidae and This and Figs.'5li-5i.3, after Wheeler. 



1 In Diptera the stomodseum may be dorsal, Dr. Pratt tells us. 



FIG. 5H. Median section of the 



