THE MONERULA. 



51 



egg-cell of animals, either before or after fertilization, the 

 original kernel disappeared. We explained this phenomenon 

 as a reversion or atavism, and assumed that the egg-cell, 

 in accordance with the law of latent heredity, first falls 

 back into the kernel-less, cytod stage (Fig. 165). It is only 

 after fertilization is accomplished that a new cell-kernel 

 arises in this cytod, which thus becomes the parent-cell 

 (Cytula, Fig. 166). The transitory kernel-less cytod-con- 

 dition, intermediate between the egg-cell and the parent- 

 cell, is an interesting germ-form, because, in accordance 

 with the fundamental law of Biogeny, it reproduces the 

 original, oldest parent-form of the Moneron; we therefore 

 call it the Monerula. (Cf. vol. i. pp. 178-183.) 



Fig. 165. — Monerula of Mammal (Rabbit). The fertilized egg-cell after 

 the loss of the nucleus is a simple ball of protoplasm {d). The outer covering 

 of the latter is formed by the modified zona pellucida (z) together with 

 a mucous layer (h) secreted on to the outside of the latter. In this a few 

 sperm -cells are still visible (s). 



Fig. 166.— Parent-cell (Cytula) of a Mammal (Rabbit): 7r, parent, 

 kernel; n, nucleolus of the latter; p, protoplasm of the parent-cell; z, 

 modined zona pellucida ; s, sperm-cells ; h, outer albuminous covering. 



