264 J. THOS. PATTERSON. 



blastopore no periblastic nuclei are present, except a few at the 

 extreme margin of the blastoderm (N). 



Fig. 9 represents the posterior portion of a section taken 

 through EF of Fig. 6. At the extreme right is the dorsal lip 

 of the blastopore (R). This lateral part of the lip is not so thick 

 as in the median section (Fig. 8, R). Below the lip is the lateral 

 portion of the blastopore. The section also passes through the 

 end of the right horn of the germ-wall (GW). The remaining 

 structures are very similar to the corresponding parts of Fig. 8 

 and need no further description. 



From Fig. 6 it will be seen that a section taken through GH 

 would no longer contain any portion of the blastopore, since in 

 this region the outer edge of the germ-wall reaches to the mar- 

 gin of the blastoderm. This section is represented in Fig. 10, 

 and its most important part, consisting of a mass of cells from 

 which the entoderm arises anteriorly, is shown at D. Between 

 this mass and the inner edge of the germ -wall there is a space in 

 which only a few cells are present. In some sections, however, 

 no such space exists, but the mass of cells is directly continuous 

 with the germ -wall. In such cases it is easy to gain the impres- 

 sion that the mass is a part of the germ-wall, and thus to be led 

 astray into concluding that the entoderm arises directly from the 

 germ-wall. A close study, however, shows that the character of 

 this mass, even in cases of its most intimate union with the germ- 

 wall, is such as to make it easy to distinguish the one from the 

 other. As previously stated, many of the cells in the region of the 

 germ-wall are directly open 'to the underlying yolk, in which 

 periblastic nuclei are present, but the cells of the mass are en- 

 tirely separated from the yolk and are completely delimited by 

 cell-walls. The significance of this mass will be considered in 

 connection with Fig. 13. 



Fig. 1 1 is a median longitudinal section of a blastoderm taken 

 thirty-eight hours after fertilization. It shows the condition of 

 the blastoderm shortly after the closing of the blastopore, and 

 clearly represents the character of the entoderm during the few 

 hours immediately following this event. It will be seen that the 

 entoderm is not a continuous layer, especially in the anterior 

 region, where the cells are more or less in groups. Later, how- 



