CYTOLOGY OF HYDRACT1NIA AND PENNARIA. 215 



somes and spherules. This gives three distinct bodies in the cyto- 

 plasm : (i) The ordinary bodies all through the cytoplasm and 

 usually interpreted as yolk masses ; (2) the coarse granules dis- 

 tributed in crescentic bands ; (3) the small bodies around the 

 periphery. The small peripheral granules remain on the outside 

 of the embryo during cleavage and can be traced into the planula. 

 In the planula they are confined to the ectoderm. The differen- 

 tiation and subsequent fate of similar particles has been made out 

 in Pennaria. The first and second class of granules are chiefly 

 confined to the mass of cells within the ectoderm of the planula, 

 although a few scattering granules are seen in the ectoderm. 



MATURATION IN Hydractinia. 



The following quotation reveals the extent of previous observa- 

 tions on this phase of development. " The ovum while in the 

 gonophore has a well-defined nucleus situated above the center 

 of the egg, which fades from view when the ovum is deposited" 

 (Bunting, page 215). "In about fifteen minutes after the ova 

 are laid the polar bodies appear. When first observed two glob- 

 ules were present, one had been extruded, while the other one 

 was just appearing. One of the two divided subsequently, in a 

 plane at right angles to the first cleavage plane of the ovum. 

 Within ten minutes from the extrusion of the first polar body, 

 the second was ejected" (Bunting, page 216). 



The nucleus during growth varies from round to elliptical and 

 in this latter shape the ends may nearly reach to the periphery 

 but until maturation begins, the nucleus is central in position. It 

 is to be regretted that more stages in maturation have not been 

 discovered notwithstanding the fact that large numbers of slides 

 have been made of eggs just after deposition. Maturation begins 

 before the eggs are discharged from the gonophore but just how 

 long I am unable to state. The fact that this process begins 

 while the eggs are still retained, makes the solving of the problem 

 tedious in as much as the gonophores are not set free as are the 

 medusae in Pennaria. Occasionally a gonophore containing eggs 

 is found among the recently discharged eggs and it was in such 

 that the first signs of maturation were detected. A large number 

 of slides were made of the large gonophores from colonies that 



