Prof. Huxley on the Phenomena of Gemmation. 215 



lation upon their nature is vain), we find that the viviparous Aphis 

 contains an organ similar to the ovarium of the oviparous female in 

 some respects, but differing from it, as Von Siebold was the first to 

 show, in the absence of what are termed the colleterial glands and 

 the spermatheca, — organs of essential importance to the oviparous 

 form. 



In the terminal chambers of this " pseudovarium," ovum-like 

 bodies, thence called "pseudova," are found. These bodies pas3 

 one by one into the pseudovarian tubes, and there gradually become 

 developed into young, living Aphides. As Morren has well said, 

 therefore, the young Aphides are produced by " the individualization 

 of a previously organized tissue." 



The only organic operation with which this mode of development 

 can be compared is the process of budding or gemmation, as it takes 

 place in the vegetable kingdom, in the lower forms of animal life, 

 and in the process of formation of the limbs and other organs of the 

 higher animals. And the parallel is complete if such a plant as the 

 bulbiferous Lily or the Marchantia, or such an animal as the Hydra, 

 is made the term of comparison. 



Thus agamogenesis in Aphis is a kind of internal budding or gem- 

 mation. If we inquire how this process differs from multiplication 

 by true ova, or " gamogenesis," we find that the young ovum in the 

 ovarium is also, to all intents and purposes, a bud, indistinguishable 

 from the germ in the pseudovarium of the agamogenetic Aphis. 

 Histologically, there is no difference between the two ; but there is 

 an immense qualitative or physiological difference, which cannot be 

 detected by the eye, but becomes at once obvious in the behaviour of 

 the two germs after a certain period of their growth. Dating from 

 this period, the pseudovum spontaneously passes into the form of an 

 embryo, becoming larger and larger as it does so ; but the ovum 

 simply enlarges, accumulates nutritive matter, acquires its outer in- 

 vestments, and then falls into a state of apparent rest, from which it 

 will never emerge, unless the influence of the spermatozoon have 

 been brought to bear upon it. 



That the vast physiological difference between the ovum and the 

 pseudovum should reveal itself in the young state by no external 

 sign, is no more wonderful than that primarily the tissue of the brain 

 should be un distinguishable from that of the heart. 



The phsenomena which have been described were long supposed 

 to be isolated ; but numerous cases of a like kind, some even more 

 remarkable, are now known. 



Among the latter, the speaker cited the wonderful circumstances 

 attending the production of the drones among bees, as described by 

 Von Siebold ; and he drew attention to the plant upon the table, 

 Ccelobogyne ilicifolia, a female Euphorbiaceous shrub, the male 

 flowers of which have never yet been seen, and which, nevertheless, 

 for the last twenty years, has produced its annual crop of fertile seeds 

 in Kew Gardens. 



Not only can we find numerous cases of agamogenesis similar to 

 that exhibited by Aphis, in the animal and vegetable worlds, but if 



15* 



