:\IATTTRAT[ON OF OVUM IN ECHINUS ESOULENTUS. 191 



sees a preparation in which both asters are cnt in the same 

 section. Griffin^ in Thalassema, has described a disappear- 

 ance of the spindle spun out between the centrosomes, and 

 the development of a central mass very like that which I 

 have described between the asters. In most instances, 

 however, the conditions are more like those described by 

 Matthews in Asterias Forbesii. 



It is evident that when the nuclear membrane disappears, 

 and the rejected chromatin passes into the cytoplasm, a pro- 

 found eifect is produced on the organisation of the egg. 

 Whereas, with the germinal vesicle still intact, the alveolar 

 structure can be traced to the surface of the egg, we now 

 find that round the transformed nucleus, and projecting into 

 the centre of the egg, is a fibrillar mass, which is sharply 

 differentiated from the alveolar yolk. From this central 

 area there also extends round the surface of the egg a layer 

 of differentiated protoplasm. The central mass and surface 

 layer have each a definite fate. The one is differentiated 

 into the spindle and asters, while the surface layer is, I 

 believe, associated with the formation of the membrane 

 thrown off by the egg at the moment of fertilisation. The 

 central mass of the yolk is unchanged in appearance, and the 

 question is whether this reticular mass of protoplasm is 

 differentiated from the cytoplasm, or is derived from the 

 rejected nuclear reticulum. I am inclined to think that it 

 is in large measure formed from, or under the influence 

 of, the discarded nuclear material. This would be in 

 harmony with the results of Carnoy and Le Brun (J 890) 

 in Triton. Another evidence of the excitement produced in 

 the egg at this stage may perhaps be seen in the accessory 

 asters formed, which, so far as I can see, have no relation to 

 the formation of the definite asters of the spindle. 



From experiments by R. Hertwig (1896) and Moi-gan 

 (189G) it seems that under special artificial chemical stimulus 

 the cytoplasm may be excited to form asters, and even, in 

 Hertwig's expei'iments, amphiasters. Reinke (1894) also 

 found that in the peritoneal cells of the larval salamander 



