212 PROF. HUXLEY ON THE AGAMIC REPRODUCTION 



§ 6. Hypothetical Explanations of Agamogenesis. 



The majority of wiiters on the wonderfvil 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 a 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 Avhich indivi- 

 duahzes 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 mth pleasui-e 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 hyj^othetical 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-ceUs, and masses of nuclei like those resvdting from the final 

 subdivision of germ-cells, retained unchanged at the filamentary extremities of the 

 branched xiterus forming the ovaria of the larval Aphides." — I. 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 o-viparous 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 Apliides, 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. 



" The condition which renders this seemingly strange and mysterious generation of an 

 embryo without precedent coitus possible, is the retention of a portion of the germ-mass 



