590 BULLETIN OF THE 



The male pronucleus arises when a living zoosperm penetrates into a mature 

 and living vitellus. In certain cases (sea-urchin) it is not much larger than 

 the " body " of a zodsperm, and one might then entertain the oj)inion that it is 

 only such a " body " swollen. It then forms the centre of an aster. In other 

 cases (Heteropoda) it becomes as large as tlie female pronucleus, and is not sur- 

 rounded by a radial figure.* This growth is not a simple inflation of the body 

 of a zodsperm by a liquid, because when fully developed it contains many 

 times the original quantity of protoplasmic substance ; it is not a process of 

 nutrition, a digestion of vitelline substance, since that physiological process is 

 complicated and requires a considerable time for its accomplishment, while the 

 absorption of vitelline substance is direct and prompt. The male pronucleus 

 is therefore a product of the union of spermatic protoplasm with vitelline pro- 

 toplasm, and from this fusion results a nuclear body possessing a multitude of 

 properties which are wanting to the isolated zoosperm. 



Likewise the female pronucleus, which has its first origin in the " corpuscules 

 de Biitschli " belonging to the internal half of the second " amphiaster de rebut," 

 is derived for the greater part from vitelline sarcode. The disproportion be- 

 tween nuclear and vitelline substances in this case is fully as great as between 

 the body of the zoosperm and the completed male pronucleus in the Hetero- 

 poda. 



Finally, the cleavage nuclei are formed at the expense of the "central 

 masses" and of the intranuclear varicosities of the old nucleus. These "masses" 

 may also descend, in part at least, from the old nucleus. But even here the 

 substance derived from that source is only a fraction of the whole mass of the 

 new nuclei. Besides, a part of the substaijce of the old nucleus remains en 

 route under the form of the " trainee internucleaire," and does not enter into 

 the composition of the new cj^oblasts. 



A consideration of the origin of the nucleus in these three cases leads to the 

 same conclusion, that its substance comes in part from a pre-existing nucleus or 

 a foreign element, and in part from the protoplasm of the cell, — the latter by 

 way of fusion, not of nutrition. The young nucleus while still quite small 

 exercises a strong influence on the surrounding vitellus. In proportion as it 

 increases in size, this influence diminishes, and once completed, it ceases to ex- 

 ist. It therefore seems permitted to conclude that the attraction or influence 

 exercised by the young nucleus increases in proportion as it is fused with cell 

 protoplasm, and subsequently diminishes when the proportion of the latter 

 element is too great. There would be a period of activity followed by a period 

 of saturation ; the latter would supervene as soon as the nucleus attained the 

 limit of its growth. 



I can omit a presentation of the author's " Theorie electrolytique des Mouve- 

 ments protoplasmiques," with which he terminates his paper, since it is not 

 directly applied to an elucidation of the phenomena under consideration. 



* The author has previously stated, I believe, that in the Heteropoda the male 

 pronucleus is surrounded by rays in the living egg. See p. 577. 



