Cii. XII] INTERPRETATIONS AND CONCLUSIONS 135 



ill wliieh such an influence could be transmitted from the nu- 

 cleus to the cytoplasm. Strasburger sujDposes the nucleus ex- 

 erts a dynamic influence on the cell-plasm. De Vries and others 

 imagine that organized particles, '"pangens," pass out of the 

 nucleus to transform the cytoplasm. Driesch suggests that the 

 nucleus secretes ferments which change the cell-plasm. These 

 hypotheses are purely imaginary, for at present we know almost 

 nothing of the function of the nucleus ; and even if we suppose 

 the differentiation comes in some unknown way from the nucleus, 

 still we do not know what could start the process in isolated 

 nuclei that are after the cleavage-period assumed to be equiva- 

 lent. There is, however, one series of experiments which seems 

 to throw some light on the present problem, although the inter- 

 pretation is extremely difficult and hazardous. I refer to the 

 experiment on the ctenophor-egg, in which a part of the cyto- 

 plasm was cut from the unsegmented egg, and the latter gave 

 rise in most cases to an imperfect embryo. Here, although the 

 entire segmentation-nucleus is present, yet by loss of cytoplasm 

 defects are produced in the embryo. The form, therefore, of 

 the early embryo Avould seem to result from the structure of 

 the protoplasm, or from the arrangement of the blastomeres 

 after cleavage. In either case the phenomenon is in the first 

 instance cytoplasmic. How can this conclusion be brought into 

 harmony with the facts, stated above, of inheritance of charac- 

 ters through the male pronucleus ? Let us assume an imaginary 

 case to show how this union of the two conceptions is possible. 

 If we had used the spermatozoon of one species (or variety) of 

 ctenophor and the egg of another species, and then after fertili- 

 zation had removed a part of the egg-cytoplasm, we should ex- 

 pect to find the embryo defective, but the organs that were 

 formed we should expect to show a combination of male and 

 female characters. In other words, the imperfect embryo would 

 have resulted from the arrangement of the protoplasm into an 

 imperfect form, but the kind of organ would have depended on 

 the structure of the nucleus in each cell. After cleavage, the 

 cytoplasm of each part differentiates into this or that organ, 

 but the kind of differentiation of each part is determined b}' the 

 nucleus of that part. 



If the argument given above should prove true, then the 



