PRELIMINARY GENERAL SKETCH 



193 



both observers independently showing that the polar spindle contains 

 distinct centrosomes, which, however, degenerate after the formation 

 of the polar bodies, their place being taken by the sperm-centrosome, 

 which divides to form an amphiaster before union of the nuclei, as 

 in RhyncJielviis. Exactly the same result has since been reached by 

 Hill ('95) and Reinke ('95) in SpJiarccJiiiuis, by Hill in the tunicate 

 Phalbisia, by Kostanecki and Wierzejski ('96) in PJiysa (Fig. 89), 

 and by Van der Stricht ('98) in Thysaiiozodn ; and in all of these the 

 centrosome is likewise shown to arise from the middle-piece or in 

 its immediate neighbourhood. Among others who have produced 



Fig. 98. — Fertilization of the egg in the copepod, Cyclops streniius. [RiJCKERT.] 

 A. Sperm-nucleus soon after entrance, the sperm-aster dividing. B. The germ-nuclei ap- 

 proaching; cf, the enlarged sperm-nucleus with a large aster at each pole; 9 , the egg-nucleus 

 re-formed after formation of the second polar body, shown at the right. C. The apposed reticular 

 germ-nuclei, now of equal size ; the spindle is immediately afterward developed between the two 

 enormous sperm-asters ; polar body at the left. 



evidence that the cleavage-centrosome stands in definite relation to 

 the spermatozoon, may be mentioned Oppel ('92) in reptiles, Brauer 

 ('92) in BrancJiipiis, Henking ("92) in insects, Riickert ('95,2) in 

 Cyclops, Sobotta ('95) in the mouse and ('98) Amphioxus, Ziegler ('95) 

 in Diplogastcr and R/iabditis, Castle ('96) in Ciona, Korschelt 

 ('95) in Ophryotrocha, Meyer ('95) in Strongyhis, Griffin ('96, '99) 

 in TJialasscma, and Coe('98) in Ccrebratidus. 



Beside the foregoing evidence may be placed the following addi- 

 tional data based on experiment and the study of pathological fer- 

 tilization, (i) In the case of sea-urchin eggs, Hertwig, Boveri, and 

 o 



