Decembek 9, 1898.] 



SCIENCE, 



829 



tion ; the second, that perspective motives 

 are operative in the neighborhood of the 

 vertical, their fui'ther influence being pre- 

 vented by the fact that the ends of the ob- 

 lique are tied to the points a and 6 ; the 

 third, that the eye, in passing along the 

 oblique, is solicited by the vertical, and the 

 more resolute effort requisite to keep to the 

 original path causes an apparent increase 

 of the angle, the curving of the line being 

 due to a conflict between the increase of the 

 acute angles and the fixity of the outer ends 

 of the oblique. 



Which of these explanations shall we ac- 

 cept? A. H. Pierce. 



Amheest College. 



SOME BEGENT AND lilPOBTANT EXPERI- 



3IENTS WITH TEE EGGS OF THE 



SEA URCHIN. 



The well-known experiments of Boveri in 

 which egg fragments were fertilized appar- 

 ently gave evidence that the union of female 

 cytoplasm with a spermatozoan may be fol- 

 lowed by segmentation and development,but 

 the proof is very inconclusive. It was left 

 for Yves Delage to complete the evidence. 



In a late communication to the French 

 Acadamy* Delage states that he has suc- 

 ceeded in dividing the egg of Strongylocen- 

 trotus lividus, not en masse by shaking, as has 

 been done heretofore, but by hand beneath 

 the microscope and in such a way that 

 there can be no doubt as to the fragments 

 obtained being parts of the same egg. He 

 was able to see that the nucleus was con- 

 tained in one part and not in the other, 

 which was, therefore, composed of ovulary 

 cytoplasm. A whole or uninjured egg was 

 placed beside the fragments and sperma- 

 tozoa introduced into the drop of water in 

 which the experiments were performed. 



Sexual attraction manifested itself with 

 equal energy by all objects. The controle 

 egg and the two fragments were fecundated. 



* Compies Bendus, CXXVII., 15 pp., 528-31. 



A little later segmentation began, appear- 

 ing first in the controle, a little later in the 

 nucleated and still later in the nonnucleated 

 fragment. The rapidity of segmentation was 

 greatest in the controle and least in the non- 

 nucleated, so that when controle was in the 

 stage 8 or 16 the nucleated fragment had 

 developed to stage 4 and the nonnucleated 

 to stage 2. In the drop of water the de- 

 velopment could not be of long duration, 

 but in one case it was successfully car- 

 ried through three days. At the end of 

 this time the controle formed a typical gas- 

 trula. The nucleated fragment had devel- 

 oped so that the only difference apparent was 

 its smaller size. The nonnucleated frag- 

 ment also developed into a gastrula, but 

 with the enteric and blastocoelic cavities 

 very much reduced, owing, no doubt, to the 

 smaller size of the fragment. In all cases 

 a vitelline membrane appeared about the 

 blastomeres. Some of the larvse were fixed 

 and stained, and the nuclei and nucleoli 

 found in the cells from the nonnucleated to 

 be no smaller than those in the cells from 

 the nucleated fragment. 



From these experiments Delage deduces 

 the following very important conclusions : 



1. The ordinary definition of fecundation 

 must be rejected as being too strict. The 

 union of the female and the male pronuclei 

 certainly takes place, but it is not essential 

 to development. 



2. Fol's conclusions as to the union of the 

 two pronunclei and of the demi-ovocenters 

 with the demi-spermoceuters must be cast 

 aside. For, as the experiments show, the 

 absence of an ovocenter is not an obstacle 

 to development. 



3. The theories in which fecundation is 

 explained, as the saturation of a female 

 nuclear polarity by a male nuclear polarity 

 must likewise be dismissed, and also those 

 theories regarding the formation of the 

 polar gobules as for the purpose of ridding 

 the female nucleus of all male elements. 



