irreproachable method by which this problem can be solved, 

 Warnek in the first published investigations on the 

 embryology of gastropodan molluscs described the first 

 period of development up to the formation of the spherical 

 multicellular stage, i.e. the blastula. Only at the end did 

 he briefly mention the following period, when "some yolk 

 globules share in the formation of first internal organ — 

 the yolk sac." This first internal organ, the yolk sac, is 

 of course nothing other than the endoderm of the embryo. 



Concerning some details of division, Warnek noted that 

 during the division of the nuclei of the yolk globules the 

 nucleolus appears earlier than the nucleus when divided into 

 two parts, therefore it is possible to find nuclei with two 

 nucleoli. Warnek never saw the process of division of the 

 nucleolus itself. The division of the nucleus in his experience 

 was always accomplished by one plan, which in the early 

 stages of divisions was the same as in the subsequent develop- 

 ment of the embryo. This division in all conditions takes 

 place after the stage of stretching of the nucleus, which 

 then acquires the shape of a biscuit and a figure eight and 

 is finally transformed into two separate nuclei. 



The globules of division Warnek identified as the 

 elementary organs, i.e. cells, and considered that their 

 multiplication, beginning at the time of division, continued 

 throughout the period of development and even through the 

 entire life of the animal. 



All the activity of the developing embryo and the 

 animal forming from it is, in Warnek' s opinion, the result 

 of that primary influence which the ovum ["yolk mass") 

 is subjected to by the semen. "This influence," Warnek 

 wrote, "has a purely chemical nature; therefore the explana- 

 tion for this is still obscure for us; the vital phenomena must 

 be given by physicists and chemists" (p . 168). "The effective 

 element in the organism," Warnek continued, 



is the material; this same material influences also 

 outside the organism. If we explain this activity by 

 chemical and physical powers, then there is no reason 

 to deny the activity of these powers in the organism 

 as well. Although these powers still cannot be 



