Dr. Burnett on the Development of Viviparous Aphides. 91 



taken into the semitransparent body of the embryo Aphis, like 

 the remnant of the yolk in the chick. I at first thought it was 

 about to be enclosed in the alimentary canal, but it was not so. 

 As the embryo grows, it assumes the position of the ovarium, and 

 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 

 progeny 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 

 Parthenogenesis, is indeed plausible and seems at first satisfac- 

 tory ; but, as I hope to show, it will not bear analysis. 



In the first place, it is evident that Owen does not recognise 

 any physiological difference between a bud and an ovum ; this is 

 clear 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 

 process/' (p. 45.) 



Here is a fundamental error, which, if not removed, will obscure 

 all our views of the physiology of reproduction. I have already 

 insisted upon the necessity of this broad distinction between 

 these two forms, — a necessity based not only upon differences 

 of anatomical constitution, but also upon physiological signi- 

 fication. An Ovum, is the exclusive product of an individual of 

 the female sex, and is always formed in a special organ called the 

 ovary. It is the particular potential representative of the female, 

 and has its ulterior development only from its conjunction with 

 a corresponding element of the opposite or male sex ; and zoology 

 presents no instance where there is development from eggs, unless 

 these conditions of the two sexes are fully carried out. 



A Bud, on the other hand, is simply an offshoot from the form 

 on which it rests, a portion of the animal capable of individual 

 development. It sustains, therefore, no relations to sex, and, in 

 truth, is widely separated in its ulterior signification from that 

 cycle of processes conceived in a true oviparous reproduction. 



All physiologists who have carefully studied embryological and 

 developmental processes must feel the correctness and importance 

 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 ar- 



