DEVELOPMENT OF PHRYGANIDS. 567 



cell protoplasm, we would expect to find a close coincidence 

 existing between the distribution of the gerra-cells and the 

 granular yolk. This is, however, not the case, for if we examine 

 sections of the eggs of Blatta cut through the longitudinal 

 dorso- ventral plane we shall find, when there are only a few 

 cells in the centre of the egg, that the deutoplasm has already 

 become granular at the periphery; later, when the cells are 

 distributed regularly throughout the egg, that a very thick 

 layer of granular deutoplasm has been formed on the ventral 

 side directly under the place of the future ventral plate. 

 Hence it would appear that the yolk transformation goes on 

 independently of the germ cells. The fact that the granular yolk 

 is found for the most part at the periphery indicates that the 

 decomposition was produced by a kind of breathing process. 

 This supposition is rendered improbable by the fact that the 

 ventral surface of the egg, which has the greatest amount of 

 granular yolk, has the least air, being turned towards the 

 centre of the cocoon in which the eggs are laid. Since the 

 transformation of the yolk is not governed entirely by the 

 supply of air, although we cannot deny that a certain amount 

 is a necessary condition, and also, since it is not produced by 

 the direct action of the living germ-cells, we must look to some 

 other agent for the conditions requisite for bringing about such 

 a transformation. Since then, the yolk is metamorphosed on 

 the ventral side, anticipating, as it were, the advent of the 

 germ-band, and supplying beforehand the necessary amount of 

 ready food for the subsequent rapid development of cells at 

 this point, it may be influenced by the same conditions which 

 determine the subsequent location of the germinal band at that 

 place. 



Stage 2. — The second stage is of comparatively short dura- 

 tion, and is marked by only two important features — the 

 formation of the blastoderm and its differentiation into the 

 ventral plate. 



The blastoderm is formed by the simultaneous aggregation of 

 a definite mass of protoplasm around each nucleus of the blas- 

 tema. These masses quickly acquire cell walls, thus forming 



