34 ON THE AGAMIC REPRODUCTION AND MORPHOLOGY OF APHIS 
late Dr. Waldo Burnett assert, with different degrees of distinctness, 
on the contrary, that there is a clear histological difference between 
the primary germs of the viviparous Apfhzs and true ova,—Carus 
and Burnett reiterating their opinions even since the publication of 
Leydig’s views. Finally, Mr. Lubbock, in his late valuable memoir 
on Daphnia (Phil. Trans. 1857) has expressed his inability to find 
any germinal vesicle in the germs of the viviparous 4fp/zs, and, so far, 
may be ranked among Leydig’s opponents. 
I have recently resumed some investigations commenced two or 
three years ago on this interesting subject. My object was originally 
purely morphological,—the Aphzs suggesting itself as a very con- 
venient subject for working out the general development of /zsecta ; 
but I have found myself unable to refrain from wandering out of my 
direct course, and attempting to further the solution of the great 
problem of Agamogenesis, or asexual reproduction. 
My observations are in the main in accordance with those of 
Leydig. On many minor points, however, we are at variance; and 
besides this, there are matters of great interest, upon which Leydig 
does not touch, but on which I hope to be able to throw some light. 
For, besides yielding an answer to the question as to the existence or 
absence of any histological distinction between a bud and an ovum, 
the investigation of the viviparous and oviparous Aphides affords 
decisive evidence as to the soundness of certain explanations of the 
phenomena of Agamogenesis in general; and finally, the study of 
the general development of Aphzs furnishes data of great importance 
in Articulate Morphology. 
I propose in the present memoir to follow out these lines of 
inquiry. I will, in the first place, describe the minute structure of 
the essential reproductive organs or “ Pseudovaria” of the viviparous 
or agamic female ; and the development of its germs or pseudova (as 
I propose to term them) will be considered. Secondly, the repro- 
ductive organs of the oviparous female and the development of the 
ova will be described. Next, I shall speak of the manner in which 
the proliferous apparatus or pseudovarium of the viviparous female 
is developed within the germ; and I shall compare together the 
agamic and sexual reproductive processes. I shall then endeavour 
by means of these facts to refute a hypothesis which has been offered 
in explanation of Agamogenesis; and, finally, I propose to con- 
sider the Morphology of the Articulata so far as it is elucidated by 
Development. 
The species of Aphis, the reproductive organs of whose viviparous 
form Iam about to describe, appeared this autumn upon a plant of 
