168 p. KtDD. 



white yolk may seem to favour the view that no distinc- 

 tion can be drawn between the two. But the structure of 

 this layer so closely resembles that of the germ, as we 

 have already more than once insisted, that we should 

 on this ground alone be justified in drawing a distinction 

 between the white yolk and the finely granular subgermi- 

 nal layer which Kolliker does not hesitate to denominate 

 protoplasmic. But the fact that nuclei are found throughout 

 this layer in all the specimens of which drawings are given, 

 is a still stronger proof that in this structure we have to deal 

 with germinal matter. If any further proof were needed we 

 might cite the case which is represented in fig. 6 to show 

 the unity of the germ and the subgerminal layer. When the 

 blastoderm is seen to be directly continuous, as in this case, 

 with the subgerminal layer, it is hard to imagine what other 

 explanation can be given than that these two different parts 

 are fundamentally of an entirely similar nature. 



It is true that Goette does state that nuclei were visible 

 in some of the projections of the floor of the subgerminal 

 cavity, but he does not state whether nuclei were found 

 throughout the extent of the floor of this cavity, and in his 

 drawings certainly does not represent such an arrangement 

 of nuclei as I have described. 



To return to the nature of the subgerminal layer. The 

 finely granular aspect which is so well marked immediately 

 beneath the segmentation cavity gradually changes to 

 a more coarsely granular appearance as it nears the white 

 yolk, and finally is replaced entirely by white yolk. But 

 does it follow because small yolk-granules are found in this 

 layer in increasing numbers towards the white yolk that 

 therefore this finely granular material is itself white yolk ? 

 We think not. What is more likely than that protoplasm 

 in contact with the food granules of the yolk should take up 

 these granules for its own nutrition ? Taking all these facts 

 into consideration, and especially relying on the presence of 

 nuclei in large numbers in this layer, we think ourselves 

 justified in regarding the subgerminal layer as essentially of 

 a germinal character. On this view the great importance of 

 this layer will be at once apparent from the part that the 

 formative cells are believed to take in the development of 

 the embryo. A study of the anatomical relations of the germ 

 and subgerminal layer in these irregular blastoderms sug- 

 gested that similar relations might obtain in the case of 

 normal blastoderms. 



Examination of normal eggs, unincubated and incubated 

 for periods as long as sixteen or eighteen hours showed that 



