ON THE AGAMIC REPRODUCTION AND MORPHOLOGY OF APHIS 55 
“parthenogenetic”? Why, finally, does not the deep substance of 
our epidermis and epithelium, which absolutely more nearly re- 
sembles embryonic tissue than the structure of the pseudovarium 
does, give rise to young? 
It may be replied, however, that the supposed “spermatic force ” 
is exhausted by the repeated subdivisions of the germ-cell before it 
becomes a part of the deep epidermic tissue; for it is one condition 
of the hypothesis, that every successive generation or series of spon- 
taneous fissions of the primary impregnated germ-cell must weaken 
the “spermatic force” transmitted to such successive generation of 
cells. 
I presume, however, that the original “ spermatic force” is at least 
as strong ina Man as in an Aphis, The average size of the embryo- 
cells in Aphzs is at least not greater than in Man, and the specific 
gravities of their essential tissues are not very different ; so that we 
may fairly assume that as many embryo-cells go to form a given 
mass of Aphis as of Man. In that case the impregnated embryo-cell 
must subdivide as often; and therefore the “spermatic force” must 
become as much exhausted in forming, say, a grain or a pound of 
Aphis, as in giving rise to the like quantity of human substance. 
In his Lectures, Professor Owen adopts the calculations taken by 
Morren (as acknowledged by him) from Tougard, that a single 
impregnated ovum of Aphis may give rise, without fecundation, to 
a quintillion of Aphzdes1 J will assume that an Apfzs weighs >, 5th 
of a grain, which is certainly vastly under the mark. A quintillion of 
Aphides will, on this estimate, weigh a quatrillion of grains. 
He is a very stout man who weighs two million grains; conse- 
quently the tenth brood alone, if all its members survive the perils to 
which they are exposed, contains more substance than 500,000,000 
stout men—to say the least, more than the whole population of 
China! And if the law cited above be correct, the “spermatic force” 
in each cell of an Aphzs of this brood must be diminished 500,000,000 
times as much as that of a single human cell; nevertheless the 
“spermatic force” of the Aphzs cell is enough to impel it to the 
production of young, while that of the human cell is not! 
When to these considerations I add, that it has been shown that 
the agamic propagation of the Ap/zs may, under proper conditions, 
be continued for four years without interruption, in which case the 
“spermatic force” in the later broods must stand in an infinitely 
minute ratio even to that contained in the cells of the tenth genera- 
1 J have not thought it worth while to add, in the products of the generations preceding 
the tenth. 
