AND MORPHOLOGY OF APHIS. 199 
gical difference between the primary germs of the viviparous Aphis 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 Aphis, 
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 Aphis sug- 
gesting itself as a very convenient subject for working out the general development of 
Insecta ; 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 vivi- 
parous 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 Aphis furnishes data of great importance in Articulate Mor- 
phology. 
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 reproductive organs of the ovipa- 
rous 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 repro- 
ductive 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 consider 
the Morphology of the Articulata so far as it is elucidated by Development. 
The species of Aphis, the reproductive organs of whose viviparous form I am about to 
describe, appeared this autumn upon a plant of the Ivy-leafed Geranium which hangs 
in my study, and for the last two months has been regularly giving rise to broods, some- 
times winged and sometimes apterous, without any appearance of males or females. — 
With respect to the external characters of the reproductive organs, I have nothing of 
importance to add to Siebold’s or Morren’s description. 
§ 2. The Development of the Pseudovum. 
The terminal chamber of any of the cæca of the pseudovarium is a rounded or oval body 
| (P.XXXVI. fig. 1, A), united by a delicate ligament (a), proceeding from its free end, with 
the ligaments which pass from the other cæca of the same side, to form the common pseud- 
ovarian ligament. Thewall of the chamber is a delicate transparent membrane (b), in which, 
here and there, rounded endoplasts (or nuclei) are imbedded ; while others lie on its inner 
