212 PROF. HUXLEY ON THE AGAMIC REPRODUCTION 
$ 6. Hypothetical Explanations of Agamogenesis. 
The majority of writers on the wonderful phenomena of Aphidian life, have been con- 
tent to state the facts more or less clearly ; but Morren, who has done this so clearly and 
philosophically, has in addition carelessly thrown out à hint of a mode of explaining 
them. The agamic Aphis, he says, is a portion of organized tissue which individualizes 
itself :— 
* Suppose that vitality is sufficiently energetic to impress, on the tissue which indivi- 
dualizes itself, the form of the producing species, and you have the generation of the 
Aphides. This energy becomes lost at the end of a certain number of generations, and 
a new impulse becomes necessary. It is that of the male. In my youth I might have 
adopted with pleasure such an hypothesis as this; but now I prefer to doubt: the facts 
which I have set forth are worth more than a theory.” 
The hypothesis is, however, to my mind, in no essential particular distinguishable 
from that hypothetical explanation which has been propounded by the author of the 
well-known work on * Parthenogenesis.” Substitute for “energy of the male,” in the 
foregoing passage, “spermatic force;" and the difference between the two hypotheses 
becomes evanescent. 
But this is a question of minor importance as compared with the value of the hypo- 
thesis in itself; and it is with regard to this latter point that I now propose to make a 
few remarks. 
Professor Owen’s views are, I believe, fairly stated in the following extracts from the 
work cited :— 
“ We find derivative germ-cells, and masses of nuclei like those resulting from the final 
subdivision of germ-cells, retained unchanged at the filamentary extremities of the - 
branched uterus forming the ovaria of the larval Aphides.”—1. c. pp. 7, 8. 
* According to my own observations, the germs are perceptible in the embryo Aphis, 
above the simple digestive sac, before any organs have been formed for their reception. 
And with regard to the nature of the organs when formed, I may remark that the con- 
tinuity of the ovarian tubes with the oviducts in all insects, is such as to render the 
negation of the term ‘ovary’ to those two bodies from which the slender extremities of 
the eight oviducal and uterine tubes proceed in the larval Aphis, to say the least, quite 
arbitrary. My examinations agree with those of Siebold, in determining scarcely any 
appreciable difference between the ovaria of the oviparous and those of the viviparous 
females. The contents of the ovarian tubes differ, inasmuch as they contain oval masses 
of granules or nuclei, comparable to the germ-mass in its state of minutest subdivision, 
in the virgin Aphides, and not ova with the germinal vesicle as in the oviparous females.” 
—Ibid. p. 38. 
“The completion of an embryonic or larval form by the development of an ovarian 
germ-cell, or germ-mass, as in the Aphis, without the immediate reception of fresh sper- 
matic force, has never been known to occur in any vertebrate animal. 
roa er which renders this seemingly strange and mysterious generation of an - 
precedent coitus possible, is the retention of a portion of the germ-mass 
