72 



One witnesses something like this in the rapid develop- 

 ment of the transverse segments of the Strobila, and their 

 almost simultaneous liberation by spontaneous fission. 



It would be needless to multiply the illustrations of the 

 essential condition of these phenomena. That condition 

 is, the retention of certain of the progeny of the primary 

 impregnated germ-cell, or in other words, of the germ-mass 

 unchanged in the body of the first individual developed 

 from that germ-mass, with so much of the spermatic force 

 inherited by the retained germ-cells from the parent-cell or 

 germ-vesicle as suffices to set on foot and maintain the 

 same series of formative actions as those which constituted 

 the individual containing them. 



How the retained spermatic force operates in the for- 

 mation of a new germ-mass from a secondary, tertiary, or 

 quaternary derivative germ-cell or nucleus, I do not profess 

 to explain ; neither is it known how it operates in develop- 

 ing the primary germ-mass from the impregnated germ- ve- 

 sicle of the ovum. In both we witness centres of repulsion 

 and of attraction antagonising to produce a definite result. 



The physiologist congratulates himself with justice when 

 he has been able to pass from cause to cause, until he arrives 

 at the union of the spermatozoon with the germinal vesicle 

 as the essential condition of development a cause ready to 

 operate when favourable circumstances concur, and without 

 which cause those circumstances would have no effect. 



What I have endeavoured to do has been to point out 

 the conditions which bring about the presence of the same 

 essential cause in the cases of the development of an em- 

 bryo from a parent that has not itself been impregnated. 

 The cause is the same in kind though not in degree, and 

 every successive generation, or series of spontaneous fissions, 

 of the primary impregnated germ-cell must weaken the 

 spermatic force transmitted to such successive generations 

 of cells. 



The force is exhausted in proportion to the complexity 



