THE CENTROSOME IN FERTILIZATION 



21 r 



Guignard's results, too, have entirely failed of confirmation by later 

 observers (p. 221), and in his own latest contribution to the subject 

 ('99) the centrosomes are conspicuous by their absence in both the 

 text and the figures. In like manner Van der Stricht's conclusions 

 have been shown by Sobotta ('97) to be without substantial founda- 

 tion, while Blanc's account, opposed to the earlier work of I^ohm, is 

 too incomplete to carry any weight. The entire case for the " qua- 

 drille " has thus fallen to the ground. In its second form the sup]:)o.sed 

 double origin of the centrosomes rests upon a single research upon 

 Ascaris by Carnoy and Le Brun ('97, 2), who assert that the cleavage- 

 centrosomes arise de novo and separately, one inside of each of tlie 

 germ-nuclei, to migrate thence out into the cytoplasm. At the close 

 of mitosis they wholly disappear, to be replaced by a new pair, like- 

 wise of intranuclear origin. Since this result is totally opposed to 

 those of Van Beneden, Boveri, Erlanger, and Kostanecki and Sied- 

 lecki on the same object, and is contradicted in the most positive man- 

 ner by Fiirst,! it may be received with some scepticism. The work of 

 Kostanecki and Siedlecki ('96) demonstrates the division of the sperm- 

 centrosome in Ascaris as described by Boveri; and while it still 

 remains possible that the daughter-centrosomes may for a very brief 

 period disappear (as in some of the mollusks described beyond), no 

 ground is given for such a conclusion as Carnoy has drawn. No one 

 familiar with the object can repress the suspicion that Carnoy and 

 Le Brun have confused the centrosomes with the nucleoli ; but only 

 renewed research can determine the point. 



The ground is now clear for a closer study of Boveri's hypothesis 

 in the light of more recent research. It should first be pointed out 

 that that hypothesis is based upon and forms a part of the more gen- 

 eral theory of the autonomy of the centrosome ; and it the latter 

 theory cannot be sustained, the a priori side of Boveri's hypothesis 

 assumes a different aspect. In point of fact the general outcome of 

 recent research on fertilization has been on the whole unfavourable to 

 the view that the cleavage-centrosomes must necessarily be intlividu- 

 ally identical with permanent preexisting centrosomes — indeed, it is 

 in this very field that some of the most convincing evidence against 

 the persistence of the centrosome has been produced. The mode of 

 origin of the cleavage-centrosomes is nevertheless a question of high 

 interest on account of the unmistakable genetic relations existing 

 between the centrosome of the spermatid and spermatozoon and those 

 of the sperm-amphiaster within the QgZ- 



There are two points of capital importance to be determined before 

 a definite decision re2:ardino: the origin of the cleavage-centrosomes 

 can be reached. First, are the centrosomes of the sperm-aster within 



i '98, p. 105. 



