72 Dr. Burnett on the Development of Viviparous Aphides. 
becomes divided into oval masses and enclosed by the filamentary 
extremities of the eight oviducts. Individual development is 
checked and arrested at the apterous larval condition. It is plain, 
therefore, that the essential condition of the development of 
another embryo in this larva is the retention of part of the pro- 
geny of the primary impregnated germ-cell.”—p. 70. 
This view of Owen, so ingeniously advanced, and which he 
has made subservient for the chief support of his new doctrine of 
Parthenogensis, is indeed plausible and seems at first satisfactory : 
ut, as I hope to show, it will not bear analysis. 
In the first place, it is evident that Owen does not recognize 
any physiological difference between a bud and an ovum ; this is 
elear from what he remarks in the first quotation, but in his work 
on Parthenogenesis he has said so in as many words. ‘“ The 
growth by cell-multiplication producing a bud, instead of being 
altogether distinct from the growth by cell-multiplication in an 
egg, is essentially the same kind of growth or developmental pro- 
cess.—p. 45. 
Here is a fundamental error which, if not removed, will ob- 
scure all our views of the physiology of reproduction. I have 
already insisted upon the necessity of this broad distinction be- 
tween these two forms, a necessity based not only upon differ- 
All physiologists who have carefully studied embryological and 
developmental processes, must feel the correctness and import- 
ance of this distinction which lies in realities and not in words. 
It is true that a bud and an ovum are composed each of the 
same elements,—simple nucleated cells; but in one, these cells 
are simply in a mass, while in the other, they have, throughout 
the animal kingdom, high or low, a definite and invariable at- 
rangement. ‘Then again as to the constitution of each and both 
being, on the whole, of nucleated . cells, it may be said, that it 
could hardly be conceived to be otherwise, for nucleated cells are 
the elementary components of all functional organized forms; 
and it may be added, moreover, that he knows little of the high- 
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