2IO FERTILIZATION OF THE OVUM 



aster containing a pair of centrosomes, on the other hand that these, 

 like the egg-centrosomes, wholly disappear from view at a later period, 

 the cleavage-centrosomes having only a conjectural origin. 



The second of the views in question is that the cleavage-centro- 

 somes are derived from both germ-cells ; and this in turn has in its 

 favour the a priori evidence that in the Infusoria conjugation takes 

 place between two mitotic figures (p. 224). It appears in two forms, 

 of which the first, though undoubtedly erroneous, has had so interest- 

 ing a history as to deserve a brief review. It was predicted by Rabl 

 in 1889 that if the centrosome be a permanent cell-organ, the con- 

 jugation of germ-cells and germ-nuclei would be found to involve 

 also a conjugation of centrosomes. Unusual interest was therefore 

 aroused when Fol, in 1891, under the somewhat dramatic title of the 

 " Quadrille of Centres," described precisely such a conjugation of 

 centrosomes as Rabl had predicted. The results of this veteran 

 observer were very positively and specifically set forth, and were of 

 so logical and consistent a character as to command instant accept- 

 ance on the part of many authorities. In the eggs of the sea-urchin 

 the sperm-centrosome and egg-centrosome were asserted to divide 

 each into two, the daughter-centrosomes then conjugating two and 

 two, paternal with maternal, to form the cleavage-centrosomes. The 

 same result was announced by Guignard ('91) in the lily, by Conklin 

 ('93) in the gasteropod Crepidula, less definitely by Blanc ('93) in the 

 trout, and still later by Van der Stricht ('95) in Amphioxus. None 

 of these results have stood the test of later work. Fol's result was 

 opposed to the earlier conclusions of Boveri and Hertwig, and a careful 

 reexamination of the fertilization of the echinoderm egg, indepen- 

 dently made in 1894-95 by Boveri (Echinus\ by myself ( Toxopneustes), 

 and Mathews (Arbacia, Asterias\ and slightly later by Hill ('95) and 

 Reinke ('95) in Sphcerechimis, demonstrated its erroneous character. 

 Various attempts have been made to explain Fol's results as based on 

 double-fertilized eggs, on imperfect method, on a misinterpretation of 

 the double centrosomes of the cleavage-spindle, yet they still remain 

 an inexplicable anomaly of scientific literature. 



Serious doubt has also been thrown on Conklin's conclusions by 

 subsequent research. Kostanecki and Wierzejski ('96) made a very 

 thorough study, by means of serial sections, of the fertilization of 

 the gasteropod Physa, and reached exactly the same result as that 

 obtained in the echinoderms. Here, also, the egg-centres degenerate, 

 their place being taken by a new pair, arising in intimate relation with 

 the middle-piece of the spermatozoon, about which forms a sperm- 

 amphiaster (Fig. 89). Conklin, after renewed research, himself 

 admitted that no quadrille occurs in Crepidula, though he still believes 

 that a union of paternal and maternal attraction-spheres takes place. 



