Regeneration in Hydroniediisae 31 



Fi.o;. 43. Single entoderm cells lying almost entirely within the 

 ectoderm. A condition sometimes found in the early stages of 

 development of the distal tentacles. Figs. 41, 42 are really the 

 completion of this process. X6oo. 



Figs. 44-60. Eudendriuui raniosinn. 44-57 X^oo; 58-60 

 X290. 



Fig. 44. \"ery early stage. Layers of ectoderm and entoderm 

 much thickened. 



Figs. 45-47, 49. Different stages in the early evagination of 

 the entoderm. 



Figs. 48-50. Transverse sections through completed or par- 

 tially completed tentacles. 



Fig. 51. Transverse sections through tentacles in dift'erent 

 stages of development. The two more or less distinct series of 

 anlagen, represent the development of the two series of mature 

 tentacles whose bases are alternately elevated and depressed. The 

 mass of polygonal cells are entoderm cells massed together in the 

 region of the hypostome. 



Figs. 52-56. Progress of development of two tentacles, from 

 the condition in which only a single cell has been pushed away 

 from the enteric cavity (fig. 56), to the complete separation of the 

 tentacles (fig. 52). 



Figs, 57, 58, 60. Longitudinal sections through the tentacles in 

 various stages of development. 



Figs. 58-60 show different stages in the development of the 

 hypostome. In Fig. 60 a considerable amount of debris is present 

 in the enteric cavity. 



In figures of Eudcndriitni ramosuni there often appear to be 

 two cells in the sections of the completed tentacle. This is due 

 to the fact that the section is not exactly transverse but has been 

 made somewhat obliquely. Where three nuclei seem to be present 

 this is due to the appearance of the nuclei of the underlying cells. 



Figs. 61-67. Pennaria tiarella. 



Figs. 61,62. Nuclei in both ectoderm and entoderm in the 

 early stages of mitosis. Xiooo. 



Fig. 63. Nearl}- completed amitotic division of an ectodermal 

 cell. Xiooo. 



305 



