AND MORPHOLOGY OF APHIS. 215 
to commence an independent life. But I ask, how does this explain agamogenesis ? 
Why does not the epithelium of the ovarium (which is as little or less changed) give rise 
to young without impregnation ? Why are not the young cells of glands, which are as 
little changed, * parthenogenetic” ? Why, finally, does not the deep substance of our 
epidermis and epithelium, which absolutely more nearly resembles 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 re- 
peated subdivisions of the germ-cell before it becomes a part of the deep epidermie 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 in a Man as 
in an Aphis. The average size of the embryo-cells in Aphis 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, Prof. 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 Aphides*. I will assume that an Aphis weighs -sth of 
à grain, which is certainly vastly under the mark. A quintillion of Aphides will, on this 
estimate, weigh a quatrillion of grains. i 
He is a very stout man who weighs two million grains; consequently 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 
Aphis 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 Aphis 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 propaga- 
ion of the Aphis 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 generation, the 
reductio ad absurdum by simple arithmetic, of the so-called explanation, appears to me to 
be sufficiently obvious. 
For the sake of argument, however, I am willing still to suppose for ogni — 
‘gamogenesis does take place in consequence of the retention of a ** spermatic force. Bat 
I must ask, how does this phrase constitute an explanation of the phenomena? Nothing 
is more common than the misuse of the word * force” on the part of ma = a 
versed in the Phraseology, than trained in the severe methods, of physical science. The 
"patient inquirer every now and then calls in the aid of molecular force, or chemical 
* I have not thought it worth while to add, in the products of the generations preceding the tenth. 
