FERTILISATION 199 



manner in the animal organisation, it is not legitimate to suppose 

 that they are definitely located in the nuclei of germ cells or in 

 any other definite parts or structures. 1 



Moreover, it should be remembered that there is no ex- 

 perimental proof that the chromosomes of the gametes are 

 the physical basis of inheritance. The only definite evidence 

 in support of this supposition appears to be Boveri's experiment, 

 in which he fertilised a non-nucleated ovum of one species of 

 sea-urchin with the spermatozoon of another species. 2 The 

 resulting pluteus or larva was purely paternal in its characters. 

 Boveri concluded, therefore, that this result was due to the 

 introduced nucleus, the maternal cytoplasm having no deter- 

 mining effect upon the offspring, but merely supplying the 

 material upon which the sperm operated. 3 Seeliger, 4 Morgan, 5 

 and others have objected to Boveri's conclusion on the ground 

 that larvae arising from cross-fertilisation show an unusually 

 wide range of variation. Moreover, Godlewsky 6 has recently 

 carried out an experiment in which he fertilised a non-nucleated 

 portion of a sea-urchin's egg with the spermatozoon of a crinoid, 

 and obtained, as a result, a larva of the maternal type. This 

 experiment seems to nullify Boveri's conclusion. 



Hickson has remarked that if it be true that the chromosomes 

 are the sole carriers of heredity it seems to be necessary to be- 

 lieve in the individuality of the chromosomes ; that is to say, 



1 The attempt to locate latent characters of organisms in particular 

 parts of the germ cells should perhaps be regarded as a survival from 

 a time when all kinds of qualities, abstract or otherwise, were supposed 

 to reside in definitely restricted positions. " Compare Phenology. The 

 centres in the nervous system are not comparable, since these are to be 

 regarded as parts of mechanisms for controlling different functions. The 

 centres preside over the respective functions, but the functions themselves 

 are not located in the centres." 



2 Boveri, " Ein Geschlechtlich erzeugter Organismus ohne Miitterliche 

 Eigenschaften," S. B. d. Gea. f. Morph. u. Phys., Miinchen, vol. v., 1889. 



3 The nuclei of such larvae have been shown to possess only half the 

 normal number of chromosomes ; see Morgan, " The Fertilisation of Non- 

 nucleated Fragments of Echinoderm Eggs," Arch. f. Entwick.-Mechanik, 

 vol. ii., 1895. 



4 Seeliger, " Giebt es Geschlechtlicherzeugte Organismen ohne Miitter- 

 liche Eigenschaften? " Arch.f. Entwick.-Mechanik, vol. i., 1894. 



6 Morgan, Zoo. cit. See also Wilson, foe. cit. 



' Godlewsky, " Untersuchungen iiber die Bastardierung der Echiniden 

 und Crinoiden-Familie," Arch.f. Entwick.-Mechanik, vol. xx., 1906. 



