CENTROSOME AXD ARCHOPLASM LV FERTILIZATION I 5/ 



forms the centre of each aster of the first mitotic figure (Van Beneden, 

 in Ascaris, '83, "87, p. 270). 



2. Each germ-cell contributes two centrosomes (or one which im- 

 mediately divides into two), which conjugate, paternal with maternal, 

 to form those of the cleavage-amphiaster (Fol, in sea-urchins, '91 ; 

 Guignard, in flowering plants, '91 ; Conklin, in gasteropods, '93). 



3. The centrosome is derived not from the spermatozoon, but 

 from the egg (Wheeler, in the case of Myzostoma, 95). 



The first of these accounts, which rested rather on surmise than 

 on adequate observation, may probably be safely rejected, for it con- 

 tradicts the universal law that the centrosome divides into two before 

 cell-division, and is unsupported by later observers (Meyer, Erlanger, 

 etc.)- The second view, as embodied in the statements of Fol, Gui- 

 gnard, and Conklin, demands fuller consideration. All these authors 

 agree that each germ-cell contributes two centrosomes, or one which 

 divides into two during fertilization. The daughter-centrosomes thus 

 formed conjugate two and two in such a manner that each of the 

 centrosomes of the cleavage-spindle is formed by the union of a cen- 

 trosome derived from each germ-cell. It is an interesting and sig- 

 nificant fact that a conjugation of centrosomes was predicted by 

 Rabl ('89) on the a priori ground that if the centrosome is a perma- 

 nent cell-organ, as Boveri and Van Beneden maintain, then a union 

 of germ-cells must involve a union not only of nuclei, but also of 

 centrosomes. Unusual interest was therefore aroused when Fol, in 

 1891, under the somewhat dramatic title of the "Quadrille of Cen- 

 tres," described precisely such a conjugation of centrosomes as Rabl 

 had predicted. The results of this veteran observer were very posi- 

 tively and specifically set forth, and were of so logical and con- 

 sistent a character as to command instant acceptance on the part of 

 many authorities. Moreover, a precisely similar result was reached 

 through the careful studies, in the same year, of Guignard, on the 

 lily, and of Conklin ('93), on the marine gasteropod Crcpidnla, a 

 confirmation which seemed to place the quadrille on a firm basis. 

 Fol's result was, however, opposed to the earlier conclusions of Boveri 

 and Hertwig, and a careful re-examination of the fertilization of the 

 echinoderm egg, independently made in 1894-5 by Boveri {Echinus), 

 by myself {Toxopneiistes), and Mathews {Arbacia, Astcrias), demon- 

 strated its erroneous character. In the echinoderm, as in so many 

 other cases, the egg-centrosome disappears. The cleavage-amphi- 

 aster arises solely by division of the sperm-aster, and the centrosome 

 of the latter is derived not from the tip of the spermatozoon, as 

 asserted by Fol, but from the middle-piece, as already described. 

 The same result has been since reached by Hill and Erlanger. 

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



