Transmission of Hereditary Characters. 473 



larva of B, 1 should know of no further objection to raise. 

 This experiment, however, would be difficult to perform. 

 Consequently Boveri's experiment, as it at present stands, 

 proves, as I have already said, only the theory of Niigeli, 

 and not that of Kolliker, Hertwig, and others. 



Lastly, I have yet to speak of one or two other experi- 

 mental investigations — " Attempts at artificial fission and 

 regeneration of Protozoa," — and to analyse the conclusions 

 which have been deduced from them. It has been shown by 

 very instructive experiments on the part of Nusbaum *, 

 Gruber f, and Balbiani \, that non-nucleated fragments pro- 

 duced by cutting-up Infusoria, even when they remain alive 

 and capable of movement for some days, are nevertheless 

 unable to feed, increase in size, and regenerate the lost parts, 

 while those fragments which contain a ])ortion of nucleus do 

 this readily. The facts in question are interesting, since they 

 prove that protoplasm is not capable of permanent existence 

 when deprived of its nucleus, just as we are unacquainted 

 with cases in which isolated nuclei are viable. But it 

 is an unjustifiable and illogical conclusion to suppose, as, 

 for instance, Weismann maintains (' Keimplasma,' p. 29), 

 that these experiments show that the nucleus is the sole 

 vehicle of heredity and the sole formative element of the 

 cell — for to say that the nucleus is indispensable for the 

 formative processes is very far from asserting that it alone 

 is indispensable. In dwelling a moment longer upon the 

 Protozoa, the following remark may be made : it is stated by 

 Kolliker (' Gewebeleiire,' p. 67) that in EugJypha the polar 

 body is attached to the nucleus. I do not know whether 

 Kolliker was led to make this assertion by his own obser- 

 vations ; he at any rate makes no mention of this. But we 

 find it stated by Schewiakoff §, who was the first to demon- 

 strate the existence of these bodies in the case of the Protozoa 

 in the Khizopod in question, that the polar bodies lie not in 

 the nucleus, but in the substance of the cell, pressed into a 

 hollow of the nuclear membrane ; and this author is also of 

 opinion that they arise, at least in part, from " the differenti- 

 ating cytoplasm." Beyond this these bodies are not yet 

 known in the Protozoa, and before their existence has been 



* M. Nusbaum, " CJeber die Tlieilbarkeit der lebendigen Materie," 

 Axc\\. f. inikr. Auat. 2(j Bd., 188G. 



t A, Gruber, " Ueber kiinstliche Theiluiig bei Infiisorien " (I,, II.), 

 Biol. Ceutralbl. 4 & o Bd. 1885. 



\ Balbiaui, " Uecherches e.xperimeutales sur la m<5rotomie des Infu- 

 soires cilies," Recueil Zool. Suisse, t. 5, 1889. 



§ Schewiakoir, " Ueber die karyokiuetische Kerntheilung der Euglypha 

 ah'eolata,'" Morphol. Jabrb. 13 Bd., 1888. 



