IN INVERTEBRATE ANIMALS. 



71 



the two new cells is smaller than the one which preceded them, yet the 

 two together occupy much more space than it did. So that at length the 

 yolk-membrane or ovum is completely filled with a mass of small cells, in 

 which the nucleus can no longer be distinguished ; and at a still later stage 

 even their cell-like form cannot be distinguished, and the mass, which now 

 begins to take the form of the young worm, seems to be composed merely 

 of granules. 



In this Entozoon Kb'lliker has distinctly observed, that the mode of 

 multiplication of the cells consists in the development of two young cells 

 within each of the cells of the preceding generation ; the parent cell then 

 undergoing solution aud disappearing. Kb'lliker believes that the deve- 

 lopment of the two new cells is dependent on the previous division of 

 the nucleus of the parent-cell, each division of the nucleus giving rise to 

 a new cell. For in the ova of Cucullanus elegans, in which the process 

 just described from Ascaris dentata is repeated, he has often observed 

 cells the nuclei of which were, in some instances, elongated, in others, 

 constricted in the middle, while in other cells there were two nuclei in 

 place of one, these two being smaller than the single nucleus of the 

 neighbouring cells, and situated, in some p^ 7.* 



cases, close together, in others, more re- 

 moved from each other (fig. 7). His opi- f^\ ,^\ /J\ ,^\ 

 nion is made more probable also, by the ^S/ 



fact of his having seen in ova of Ascaris dentata, two small nucleated 

 cells enclosed within a parent-cell which had no nucleus (see fig. 8, C). 



Fig. 8. f 



* Fig. 7. Cells from ovum of Cucullanus elegans, shewing supposed division of the 

 nucleus in the manner just described. (After Kolliker.) 



t Fig. 8. A, B, C, D, successive stages of the ovum of Ascaris dentata, shewing duplica- 

 tion of cells. E, F, G, H, ovum of Cucullanus elegans, shewing the advance of the process. 

 (After Kolliker.) 



