THE HISTORY OF ANATOMICAL SCIENCE 329 



is an interesting circumstance that the leading 

 idea of ' Parthenogenesis ; ' namely, that sexless 

 proliferation is, in some way, dependent upon the 

 presence, in the prolifying region, of relatively un- 

 altered descendants of the primary impregnated 

 embryo cell (A + B) — is at the bottom of most of 

 the attempts which have recently been made to 

 deal with the question. The theory of the con- 

 tinuity of germ-plasm of Weismann, for example, 

 is practically the same as Owen's, if we omit from 

 the latter the notion that the endowment with 

 4 spermatic force ' is the indispensable condition 

 of proliferation. The great progress of knowledge, 

 about these matters, since 1849, lies in the demon- 

 stration of the importance of a certain formed 

 material which is met with in the nuclei of cells ; of 

 the fact that this substance, growing and dividing, 

 is distributed from the nucleus of the primary cell 

 to the nuclei of all the cells of the organism ; that, 

 in sexual proliferation, the nuclear substances of 

 A and B pass, bodily, into the nucleus of the 

 resulting embryo cell, without losing their inde- 

 pendence, and are similarly transmitted to all the 

 cells of the adult ; whence it follows, that every 

 histological element of the adult living body thus 

 produced contains associated, but yet materially 

 distinct, descendants of the nuclear elements de- 

 rived from each parent. 



This discovery ranks, in my judgment, as the 

 greatest achievement of morphological science 



