CRITICISM OF Owen's theory. 323 



ovum, whether the ovum be fertilised or not ; and 

 farther, that the " yolk cells " are not cells at all. On 

 this latter point it may be observed that embryologists 

 are still divided,* the dispute turning on the correct 

 definition of a cell — much as if men disputed whether 

 a book " in sheets " ought properly to be called a "book." 

 As regards Owen's theory, a sliglit modification in its 

 terms would meet the objection. 



Not so the objection which must, I think, be raised 

 against the vital point in the theory — the assumption 

 of a definite prolific force contained in the primary 

 germ-cell, a force which becomes diluted by subdivision 

 of the cell, and can be renewed only through another 

 act of fertilisation. This is the heel of Achilles ; if 

 vulnerable here, our theorist may be pricked by any 

 vulgar javelin. Let us try. " The physiologist," says 

 Owen, " 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 embryo from a parent that has 

 not itself been impregnated. The cause is the same in 

 kind, though not in degree ; and every successive gene- 



* See the latest work on the subject : Funke's Lehrhuch der Phy- 

 siologie, p. 1366 et seq. 



