80 



J. Thos. Patterson. 



cavity, which we may now call the subgerminal cavity. ^^ At the 

 posterior end (Fig. 29, p.) the blastoderm is only a single cell thick, 

 but towards the anterior it gradually increases in depth. Although 

 the anterior fourth of the disc is at least six cells deep, yet distinct 

 layers can not be made out, but the cells are more or less loosely 

 arranged. In the enlarged drawing of the anterior end the details 



Fig. VI. A diagrammatic reconstruction from camera drawings of the 

 sections of a blastoderm talcen about tbirty-tliree hours after fertilization. 

 The lines CR, 'NF and UK are the planes of sections of Figs. 29 (or 2 

 and 3), 4 and 5 respectively. The zone of junction {z) is all but completely 

 interrupted at the posterior margin, x 27.2. 



of the zone of junction are shown (Fig. 2, PL I, z). Cells in every 

 stage of formation are present, and at ce is one completely formed 

 about a periblastic nucleus, and toward the ccmter are several others 

 undergoing the same process. The whole region from the letter z 

 to the left end of the drawing is a syncytium — a region containing 

 many periblastic nuclei. 



"Although the term subgerminal cavity is here used in the sense in which 

 it is usually employed, namely, to designate an enlarged segmentation cavity, 

 yet it should he said that from the standpoint of comparative embryology, it 

 has little or no significance. 



