AND MORPHOLOGY OF APHIS. 211 
which gives rise to the true egg. The pseudovum is detached from the pseudovarium in 
the same way as the ovum from the ovarium. In both cases, the act of separation is in 
every respect a process of gemmation. : 
From this point onwards, however, the fate of the pseudovum is different from that of 
the ovum. The former begins at once to be converted into the germ ; the latter accu- 
mulates yelk-substance, and changes but little. Both bodies acquire their membranous 
investment rather late; within it the pseudovum becomes a living larva, while the ovum 
is impregnated, laid, and remains in a state of rest for a longer or shorter period. 
Although, then, the pseudovum and the ovum of Aphis are exceedingly similar in 
structure for some time after they have passed out of the condition of indifferent tissue, 
it cannot be said that the sole difference between them is, that the one requires fecundation 
and the other not. When the ovum is of the size of a pseudovum which is about to 
develope into an embryo, and therefore long before fecundation, it manifests its inherent 
physiological distinctness by becoming, not an embryo, but an ovum. Up to this period 
the influence of fecundation has not been felt; and the production of ova instead of pseud- 
ova must depend upon a something impressed upon the constitution of the parent before 
it was brought forth by its viviparous progenetrix. 
In this respect, the ova of Aphis exhibit the same relation to the pseudova as the 
ephippial eggs of Daphnia (whose development has been so well described by Mr. Lub- 
bock) bear to the agamic eggs; for the histological change in the ovarium of Daphnia, 
which precedes the development of the ephippial eggs, is clearly shown by Mr. Lubbock 
to have no relation to fecundation. 
Let me remark on yet another interesting, though perhaps only partial, analogy. Von 
Siebold has shown that the ova of the Queen bee produce females or males, according as 
they are fecundated or not. The fecundated ovum produces a queen or a neuter accord- 
ing to the food of the larva and the other conditions to which it is subjected; the un- 
fecundated ovum produces a drone. Now, what have we seen in Aphis? The fecun- 
dated ege produces viviparous Aphides, which are the equivalents of the neuter bees ; 
and from them are eventually produced males and oviparous females. The oviparous 
females are fecundated and lay eggs which produce only viviparous or neuter Aphides. 
On the view which Dr. Carpenter and myself take of the zoological individual, the 
whole produce of a single fecundated ovum of the Aphis is as much the Aphis individual 
as it is the Bee individual. Consequently we have two equivalent and related series. 
å äi Ova requiring impregnation, and males. 
Bee, Impregnated ova : Neuters or females roducing4 Females which give rise to ova requiring 
Aphi producing 4 |... P à 
phi. Impregnated ova Viviparous neuters impregnation, and males. 
The fact that in the one case the males are developed from pseudova —€— fully- 
formed true ova, "and: in the other from pseudova resembling — " 
Makes no essential difference in the analogy, but only demonstrates pe CR 
impossibility of drawing any absolute line of demarcation histologically between ova 
and buds. 
VOL. XXII. T 
