GENEOLOGICAL. 389 



parthenogenetic in natural conditions, but this is 

 only a supposition and will not, even if verified, af- 

 fect the interest of Loeb's experiments. 



(h) Boveri's Experiment. — The brothers Hert- 

 wig showed that non-nucleated fragments of a sea- 

 urchin's egg might be ^^ fertilised " by a spermato- 

 zoon, and might segment. In 1889, Boveri proved 

 that they might form dwarf larva^, and Morgan in 

 1895 demonstrated that the nuclei of such larva? con- 

 tained only half the normal number of nuclear ele- 

 ments or chromosomes, — an indication of the fact 

 that the nuclear material was wholly paternal, i.e., 

 derived from the sperm-nucleus. 



" Now, by fertilising enucleated egg-fragments of 

 one species (Sphcerechinus granulans) with the sper- 

 matozoa of another (Echinus tuherculatus), Boveri 

 obtained in a few instances dwarf Plutei (larvae) 

 showing except in size the pure paternal characteristics, 

 i. e., those of the Echinus. From this he concluded 

 that the maternal cytoplasm has no determining effect 

 on the offspring, but supplies only the material in 

 which the sperm-nucleus operates. Inheritance is, 

 therefore, effected by the nucleus alone. 



"The later studies of Seeliger (1894), Morgan 

 (1895), and Driesch (1898), showed that this result is 

 not entirely conclusive, since hybrid larvae arising by the 

 fertilisation of an entire ovum of one species by a sper- 

 matozoon of the other show a very considerable range 

 of variation; and while most such hybrids are inter- 

 mediate in character between the two species, some in- 

 dividuals may nearly approximate to the characters of 

 the father or the mother. Despite this fact, Boveri 

 (1895) has strongly defended his conclusion, though 

 admitting that only further research can definitely de- 

 cide the question." * 



* E. B. Wilson, The Cell in Development and Inheritance^ 

 2nd ed., l&OO, p. 353. 



