THE SUPERFICIAL AND THE IMMERSED GERM-BAND. 



273 



envelopes, as well as the position of the former, differ still further 

 from those which we described above, and which we took as a 

 starting-point for the sake of clearness. "We must now deal with 

 all these conditions in detail. 



From the above description of the rise of the amniotic fold 

 (Figs. 132 and 133, of), it becomes evident that a cavity, con- 

 tinuous with the space containing the food-yolk, extends in between 

 the serosa and the true amnion. It is thus possible for spherules 

 of food-yolk to pass into this cavity and entirely to fill it (Fig. 135). 

 In this case the amnion and the serosa are separated from each 

 other by a somewhat wide space filled with food-yolk, whereas, 

 in other cases, where the food-yolk does not penetrate this cavity, 



-n 



Fig. 135.— Section through the germ-band of a Lepidopterovts Insect (combined from drawings 

 by Bobretzky and Hatschrk). ah, amniotic cavity ; am, amnion ; c, coelomic cavity ; do, 

 food-yolk (divided up into separate masses, each containing a nucleus) ; cc, ectoderm ; 

 m, mesoderm ; pr, thickenings of the ectoderm, representing the rudiments of the ventral 

 nerve-cords ; s, serosa. 



the amnion and the serosa are in direct contact (Fig. 158 B-F). 

 "We may thus divide the eggs of Insects into two groups, according 

 to the presence or absence of this space between these two embryonic 

 envelopes. 



1. Eggs in which the germ-band is superficial, i.e., in which the 

 elements of the food-yolk have not penetrated into the space between 

 the amnion and the serosa. The germ-band is here comparatively 

 superficial (Figs. 132, p. 267; 133, p. 269; 140 A, p. 281; 143, 

 p. 286). 



2. Eggs in which the germ-band is sunk or Immersed, the space 

 between the amnion and serosa being filled by particles of food-yolk. 

 In such cases the germ-band appears, as compared with type 1, more 

 deeply sunk within the egg (Figs. 135, 136 C-E, and 142, p. 285). 



