50 ON THE AGAMIC REPRODUCTION AND MORPHOLOGY OF APHIS 
changes but little. Both bodies acquire their membranous invest- 
ment 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. Aphzs are ex- 
ceedingly 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 develop 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 pseudova 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 Aphzs exhibit the same relation to the 
pseudova as the ephippial eggs of Daphnia (whose development has 
been so well described by Mr. Lubbock) bear to the agamic eggs ; 
for the histological change in the ovarium of Dephuia, which pre- 
cedes 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 according 
to the food of the larva and the other conditions to which it is sub- 
jected ; the unfecundated ovum produces a drone. Now, what have 
we seen in Aphis? The fecundated egg 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 Apf7s individual as it is the Bee individual. 
Consequently we have two equivalent and related series. 
Ova requiring impregna- 
tion, and males. Females 
which give rise to ova 
ut; II. 
Bee. Impregnated ova q__ pro- j Neuters or females) pro- 
Aphis. Impregnated ova § ducing { Viviparous neuters § ducing os : 3 
requiring impregnation, 
and males. 
