Hargitt: Pennaria tiarella and Tubularia crocea. 



PLATE 8. 



Tubularia crocea. 



Fig. 61. Early cleavage similar to Figure 60, but with equatorial cleavage 

 furrows already started. Corrosive-acetic, iron hematoxylin. 

 X 51. 



Figs. 62a, 62b. Two sections of one egg, which contained 30 nuclei, similar 

 to Figure 61. The elongated shape of the egg is probably due to 

 pressure in the gonophore. Pseudo-cells not represented. Cor- 

 rosive-acetic, picro-hematoxylin. X 51. 



Fig. 63. Blastula composed of 40-50 cells. Some of the spindles are radial, 

 indicating the beginning of a primary delamination. The result 

 is the formation of the germ layers and the obliteration of the 

 segmentation cavity. Pseudo-cells still abundant, but not 

 shown. Corrosive-acetic, iron hematoxylin. X 51. 



Figs. 64, 65. To show nuclear proliferation and the beginning of cytoplasmic 

 division. The drawings represent the middle sections of two 

 eggs upon which all nuclei are projected. In Figure 64 nuclei 

 in four pairs on one side of the egg; a polar cell (cl. pol.) and cyto- 

 plasmic furrow occur at the same pole. In Figure 65 the nuclei 

 are more scattered. Zenker's fluid (Fig. 64), Flemming's fluid 

 (Fig. 65). Iron hematoxylin and Congo red. X 51. 



Fig. 66. An egg from the same polyp as the preceding, with a more regular, 

 though unequal, cleavage. Zenker's fluid, iron hematoxylin 

 and Congo red. X 51. 



Fig. 67. Late stage in nuclear proliferation, cytoplasmic division in progress; 

 a segmentation cavity present. Flemming's fluid, iron hema- 

 toxylin and Congo red. X 51. 



Fig. 68. Very late stage, in which a solid mass of cells is present; cytoplasmic 

 division still retarded. Zenker's fluid, iron hematoxylin and 

 Congo red. X 51. 



Fig. 69. More regular cleavage, in which the segmentation cavity is being 

 filled by cells, — a part of the process of germ-layer formation. 

 Corrosive-acetic, Ehrlich's hematoxylin and eosin. X 51. 



Fig. 70. Blastula double, perhaps the result of an uncompleted first cleav- 

 age. Germ layers forming. Pseudo-cells still abundant, but 

 not shown. Corrosive-acetic, picro-hematoxylin. X 51. 



