EX ESOMPERIMECNTS OEDITIN- VISION. 



269 



pendent of the nucleus, (b) in the presence of two asters instead of one and 

 (c) not only along the cleavage plane but also at the polar region (cf. 

 CoNKLiN '03 p. 94). In this connection it may be mentioned that I have 

 met with several cases, in which short blunt knots appeared along the 

 cleavage furrows of the first division, e.g., Fig. 18 (cf. Rhumbler '04 pp- 

 60, 68, 69; Boveri '03 p. 3 ; Jolly '04 pp. 504, 505). 



b. without the aster. 



Case 13. An egg was cut horizontally at an anaphase of the first divi- 

 sion (Fig. 3). The nucleated fragment divided normally. No asters 

 appeared in the enucleated fragment. The cleavage-furrow at the vegetal 

 pole of the latter remained as when it was cut, whereas a new furrow was 

 formed on the cut surface. The rate of growth of this furrow was much 

 slower than that in the uncleated fragment. After seven minutes cleavage 

 went on as in the egg of ctenophores (Fig. 4). In three hours the enu- 

 cleated piece was found completely divided in two (Fig. 5). Each 

 " blastomere " has a pear-shape with a protuberance at the vegetal pole. 

 This clearly shows that an enucleated egg-fragment divides itself with the 

 aid of neither the nucleus nor the aster, provided that it be in a state of 

 division-activity. I wachted this fragment to see if that showed any periodi- 

 cal activity as in the polar lobe of the egg of Dentalium (Wilson '04 pp. 

 52, 54, 55), but this did not occur. 



Case C. An egg was cut at the two-cell stage horizontally (Fig. 7). 

 In a quarter of an hour the nucleated piece divided in four blastomeres (Fig. 

 6). No asters were seen in the enucleated fragment. It was, however, 

 found constricted in the middle. This may be taken for an unsuccessful 

 attempt of division. 



Case D. The operation was the same as C (Fig. 9). Each half of 

 the enucleated fragment assumed a pear-shape with its pointed end to- 

 wards the vegetal pole strikingly resembling Fig. 5 (Fig. 10). 



Case E. An egg was cut at the two-cell stage vertically (Fig. 11). 

 No asters developed in the enucleated fragment. The egg proper divided 

 fairly normally. The enucleated fragment elongated and had a deep con- 



