DEVELOPMENT PRIOR TO LAYING 59 



germ-wall by the area with large granules Y. These zones con- 

 stitute the opaque area. The circles in the pellucid area represent 

 megaspheres, that is yolk-masses cut off from the floor of the 

 subgerminal cavity and lying in the latter (cf. Fig. 28 M). The 

 invaginated entoderm is represented by the crossed area E; 

 the lip of the blastopore, where ectoderm and entoderm are 

 continuous, by the region R. 



FIG. 31. A diagrammatic reconstruction of the blastoderm repre- 

 sented in Fig. 30. (After Patterson.) 



R., Mass of cells left after closure of blastopore. S.G., Anterior 

 portion of subgerminal cavity not yet crossed by the entoderm. Other 

 abbreviations as in Fig. 29. 



The last three or four hours prior to laying witness the closure 

 of the blastopore. A comparison of Figs. 27 and 29 will show 

 that the blastopore has become considerably narrower in the 

 later stage. It will be observed that the posterior ends of the 

 germ-wall are approaching. Finally they come into contact, and 

 the blastopore is closed. During this process the lip of the 

 blastopore is not cut off externally, but on the contrary comes 



