. Journal of morphology . 06, also con-tribute to the vascular tissues. The inner edge of this lower layerbecomes united to the free margin of the invaginated entoderm, whenthe latter spreads over the subgerminal cavity sufficiently to meet first place for this union to occur is necessarily at the postero-lateral regions, and the last place is at the anterior end of the cavity. Sections taken slightly to either side of the median line are ofinterest, in that they have vacuoles or cavities in the dorsal lip Gastrulation in the Pigeons Egg. 99 (Figs. 38 and 39). The position of the caviti
. Journal of morphology . 06, also con-tribute to the vascular tissues. The inner edge of this lower layerbecomes united to the free margin of the invaginated entoderm, whenthe latter spreads over the subgerminal cavity sufficiently to meet first place for this union to occur is necessarily at the postero-lateral regions, and the last place is at the anterior end of the cavity. Sections taken slightly to either side of the median line are ofinterest, in that they have vacuoles or cavities in the dorsal lip Gastrulation in the Pigeons Egg. 99 (Figs. 38 and 39). The position of the cavities suggests that theyare probably to be regarded as the remains of the cavity that wasformed between the upper and lower layers when the former turnedunder to give rise to the latter. I might suggest that there isanother possibility, namely, that such cavities are the homologue ofKupffers Vesicle. Fig. 40, which is from a section taken through the plane KF ofFig. XI shows the tip of the right horn of the zone of junction. Fig. XII. Reconstruction of a blastoderm taken thirty-six and one-fourthhours after fertilization. Lettering is the same as in Fig. XI, FH, planeof section represented in Figs. 20 and 21. The numbers within the areasformed by the four intersecting lines indicate the number of degeneratingperiblastic nuclei in these areas, x and the lateral part of the dorsal lip. The length of the lip in sec-tion becomes less and less in passing laterally, finally disappearingaltogether. Thus in Fig. 41 it is no longer present, and the marginis occupied by the zone of junction, inside of which is a region whoseposition would lead one to call it germ-wall, but it is probably morecorrect to regard it as a portion of the lip that has already beenenclosed within the horns of the zone. Passing still farther to the 100 J. Thos. Patterson. side one finds the posterior margin becoming less thick and gradu-ally taking on the syncytial condition characteristic of the anteriorand l
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