DEVELOPMENT. 



189 



diaphragm (fig. 110, D] consisting of a layer of flattened cells ;* 

 other cells (fig. 109) pass into and through the walls of the 

 somites, and reach their central cavity, where they increase in 

 number and blend with the mesoblast cells. What finally 

 becomes of them I cannot say ; perhaps they form the fat-body. 



D 



M 



Ap 



Fig. 110. Transverse section through ventral region of Embryo of B. germanica. The 

 nerve-cord has by this time detached itself from the epiblast, E. D is the temporary 

 diaphragm ; Ch, temporary cellular band, from which the neurilemma proceeds ; 

 Ap, appendages in section; M, mesoblast; N, nerve-cord. (Oc. 4. Obj. BB. 

 Zeiss). 



The ventral plate occupies, as I have explained, the future 

 ventral surface of the Insect, and here only at first both the 

 embryonic membranes are to be met with. On the sides and 

 above the yolk is invested by the serous envelope alone. The 

 ventral plate, however, gradually extends upwards upon the 

 sides of the egg, in the directions of the arrows (fig. 107), and 

 finally closes upon the dorsal surface of the embryo, so as com- 

 pletely to invest the whole yolk. Every segment of the 

 embryo shows at a certain stage numerous clusters of spherical 

 granules, which according to Patten (loc. cit.) are composed of 

 urates (fig. Ill, 8). 



* Cf. Korotneff, Embryol. der Gryllotalpa. Zeits. f. wiss. Zool. (1885). 



