Hargitt: Pennaria tiarella and Tubularia crocea. 



PLATE 9. 



Tubularia crocea. 



All figures are from blastulae, or from embryos forming the germ layers, 

 and show the double nuclei characteristic of those stages. Corrosive-acetic, 

 iron hematoxylin. X 2250. 



Fig. 71. Primitive entoderm cell in resting condition. 

 Fig. 72. Primitive ectoderm cell in resting condition. 

 Fig. 73. Primitive entoderm cell in resting condition, showing the persistent 



interzonal filaments of the preceding cell division. 

 Fig. 74. Entoderm cell. Spindle of an approaching division forming, and 



interzonal filaments of the preceding division still present. 

 Fig. 75. Ectoderm cell with the chromosomes formed independently in the 



two parts of the nucleus. 

 Fig. 76. Entoderm cell similar to Figure 75, but having two centrosomes and 



asters. 

 Fig. 77. Portion of an ectoderm cell showing recently completed nuclear 



division, interzonal filaments still visible and each daughter nu- 

 cleus composed of two vesicles. 

 Fig. 78. Polar view of chromosomes in daughter plate, not in two groups. 



From a cell early in the formation of the germ layers. 

 Fig. 79a-79e. Polar views of five equatorial plates in the division of ectoderm 



and entoderm cells of the germ layers, showing arrangement of 



chromosomes in two groups. 



