1897.] NEW YORK ACADEMY OF SCIENCES. 377 



Biological Section. 

 Meeting of December 13th, 1897. 



Professor Stratford in the chair. 



Thirty-eight persons present. 



The following program was presented : 



E. B. Wilson, Considerations on Cell Lineage, based on a Re- 

 ■examination of some points in the Development of Annelids and 

 Polyclades. The paper will appear in the Annals, Vol. XI. 



H. E. Crampton, The early History of the Egg in Molgula 

 Blanhaltenis. 



Professor Wilson's paper dealt with the origin and relations 

 of the mesoblast in Annelids and Polj'clades to show that an- 

 ■cestral reminiscence may be represented in cell lineage. The 

 mesoblastic pole cells of Annelids and MoUusca are to be re- 

 garded historically and ontogenetically as derivatives of the 

 archenteron, the two rudimentary cells in Aricia and Spio being 

 vestiges or ancestral reminiscences of such origin. The meso- 

 blast of Polyclades is of ectoblastic origin and points to the 

 suggestion that the origin of mesenchyme cells from the second 

 quartet in Unio and Crepidula, or from the third quartet in 

 Physa and Planorbis, may be an ancestral reminiscence of the 

 mesoblast formation in the Pol3'clades. 



Mr. Crampton reported that a true " yolk-nucleus " is found 

 in the oocj^te of Molgula Manhattensis ; that it is probably de- 

 rived from the nucleus and that it gives rise to the later yolk 

 spherules. The 3'olk nucleus is probably an albuminoid body 

 closely allied to 3'olk or deutoplasm, as shown by a number of 

 microchemical tests. The first maturation spindle arises en- 

 tirely from the germinal vesicle and is without centrosome and 

 asters. The first polar body receives sixteen chromosomes, 

 while sixteen remain in the egg. The second polar bodj- re- 

 ceives only eight chromosomes. The division of the first cleav- 

 age spindle was briefi}' described. 



Mr. Crampton's paper was discussed b}- Professor Bristol, 

 Professor W ilson and others. 



The Section adjourned at 10:15. 



Gary N. Calkins, Secretary. 



