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 
‘ 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 ot 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 
