Minot.] 170 [April 18, 



branchs, Flemming ; perch and chick, Oellacher) that the finely gran 

 ulate protoplasm is at first distributed around the whole egg, and 

 subsequently only collects at one pole. 



It is possible therefore that every egg consists, like a protozobn, of 

 an endoplasm and ectoplasm. In this connection it becomes partic- 

 ularly interesting to call attention to another resemblance between 

 eggs and Infusoria. Engelmann and Biitschli by supplementing the 

 observations of one another, have made evident the real nature of 

 the process of reproduction in the Infusoria, showing that the so- 

 called nucleolus acts as a male element, passing with a little proto- 

 plasm at the time of conjugation into another infusorium, which 

 usually reciprocates the process. After conjugation the Infusoria 

 both go on dividing asexually for several generations, apparently 

 until they become so exhausted that a new conjugation is necessary. 

 Now in the case of eggs, impregnation, as has been abundantly 

 proven by the recent observations of Hertwig, Eld. van Beneden and 

 Fol, is effected by a spermatozoon entering the yolk, where it unites 

 with the nucleus (female pronucleus), upon which the egg divides 

 into numerous cells, just as in the Infusoria, with this difference only 

 that the cells remain together instead of separating to form inde- 

 pendent individuals. Now, in the case of the Infusoria the animal 

 prepares for impregnation by throwing out its own male element, or 

 a nucleus with a little protoplasm — eggs prepare to receive the 

 spermatozoon by ejecting as direction-cells (Richtungsbldschen, glob- 

 ules polaires) a nucleus with a little protoplasm. The Richtungsblds- 

 chen are comparable to the nucleoli of Infusoria. A further confirma- 

 tion of this homology is offered by the formation of the "Kernspindel," 

 as introductory alike to the ejection of the direction-cells and the 

 expulsion of the nucleoli (Biitschli, Hertwig, Fol, Flemming). We 

 distinguish therefore equally in both cases the formation of a genera- 

 tion in which the two sexes are separate cells, and then the union of two 

 sexual unicellular individuals, of different origin, to form an asexual 

 cell, which then goes on dividing asexually for many generations until 

 the original energy is exhausted. The sexual generation may be 

 called genoblasts, the female arsenoblasts, the male thelyblasts (direc- 

 tion cells, nucleoli of Infusoria and spermatozoa). It therefore 

 appears that a real alternation of generations occurs throughout the 

 animal kingdom — a law which is already well established for plants 



In accordance with the view just advanced, the egg becomes really 



