68 RE GENERA TION 



pieces may be due to a lack of oxidation. The nucleus contains 

 substances which, according to Spitzer, are favorable to the process 

 of oxidation. When the nucleus is removed, the oxidation is sup- 

 posed by Loeb to be too low to allow the process of regeneration to 

 take place. In support of this view, he points out that while non- 

 nucleated pieces of infusoria live for only two or three days, non- 

 nucleated pieces of plants containing chlorophyl may be kept alive 

 for five or six weeks. Non-nucleated pieces containing chlorophyl 

 can obtain a supply of oxygen, owing to the breaking down of carbon 

 dioxide in the chlorophyl-bodies, and the consequent setting free of 

 oxygen. It should be pointed out, on the other hand, as opposed to 

 Loeb's view, that non-nucleated pieces of amoeba have been kept 

 alive for fourteen days ; and that despite the better oxidation that 

 may take place in non-nucleated pieces of plants, regeneration does 

 not take place. 



It has been found that non-nucleated pieces of the egg of the 

 sea-urchin do not segment or develop, and the result is the same 

 whether the pieces come from fertilized or unfertilized eggs. If, 

 however, a spermatozoon enters one of these pieces, the piece will 

 segment, and, as Boveri and later Wilson have shown, it will produce 

 an embryo. 



Boveri also tried fertilizing a non-nucleated piece of the egg of 

 one species of sea-urchin with a spermatozoon of another species. 

 He found that the embryo that develops is of the type of the species 

 from which the spermatozoon has come, and he concluded that the 

 nucleus determines the character of the larva, and that the protoplasm 

 has no influence on the form. The evidence from which Boveri 

 drew his conclusion is not beyond question. It has been shown by 

 Seeliger ('95) and myself ('95) that if whole eggs of the species 

 SphferccJiinns granularis, used by Boveri, are fertilized by the sper- 

 matozoa of the other species, Echinus microtuberculatns, there is 

 great variability in the form of the resulting larvae. Most of them are 

 intermediate in character between the types of larvae of the two 

 species, but a few of them are like the paternal type. Vernon ('99) 

 has more recently shown that the character of hybrids is dependent 

 upon the ripeness of the sexual products of the two parents. If, 

 for instance, the eggs (sphaerechinus) are at the minimum of maturity, 

 the hybrids are more like the male (strongylocentrotus). 



It remains, therefore, still to be shown whether or not the proto- 

 plasm has any influence on the form of larva that comes from a non- 

 nucleated piece, fertilized by a spermatozoon of another species. 

 That the nucleus of the male does have an influence on the form of 

 the animal is abundantly shown by the inheritance of the peculiarities 

 rf the father through the chromatin of the spermatozoon. 



