EXPERIMENTS ON THE ORIGIN OF THE 

 CLEAVAGE CENTROSOMES. 



EDWIN G. CONKLIN. 

 (From the Zoological Laboratory of the University of Pennsylvania.) 



The great diversity of opinion as to the origin of the cleavage 

 centrosomes which appear during the fecundation of the egg is 

 well known to all students of cytology. By different authors 

 every possible view has been held with regard to the source of 

 these centers, as may be seen from the following classification : 



1. The cleavage centrosomes come from the sperm centro- 

 some ; Boveri ('87, '92, '95), Vejdovsky ('88), Fick ('93), Wilson 

 and Mathews ('95), Hill ('95), Mead ('95), Reinke ('95), Kos- 

 tanecki and Wierzejski ('96), Kostanecki and Siedlecki ('96), 

 Sobotta ('97), MacFarland ('97), Erlanger ('97), Griffin ('99), 

 Coe ('99), Linville (1900). 



2. The cleavage centrosomes come from the egg centrosome ; 

 Van Beneden ('87), Wheeler ('95) ; all cases of normal and arti- 

 ficial parthenogenesis. 



3. The cleavage centrosomes come from both egg and sperm 

 centrosomes; Fol ('91), Guignard ('91), Blanc ('93), Conklin 

 ('94), Carnoy and Lebrun ('99). 



4. The cleavage centrosomes come from neither egg nor 

 sperm centers but are new formations ; Foot ('97), Lillie ('97), 

 Child ('97), Mead ('98).' 



It is probable that some of these conflicting views may be 

 attributed to erroneous observations, and the writers who have 

 maintained the first view have in general explained all others as 

 due to this one cause, but on the other hand some of the evi- 

 dence in favor of these other views cannot be thus lightly brushed 

 aside. As long as this question remained on a purely observa- 

 tional basis no one seems to have seriously considered that there 

 might be an element of truth in more than one of these views 

 and that the cleavage centrosomes might arise differently in differ- 



1 For references see Wilson, " The Cell in Development and Inheritance," 1900. 



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