ON THE PHENOMENA OF GEMMATION 323 



In the terminal chambers of this " Pseud-ovarium," ovum-hke 

 bodies, thence called " pseud-ova," are found. These bodies pass 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 bulbi- 

 ferous 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 

 gemmation. 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 

 investments, 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 undistinguishable from that of the heart. 



The phenomena 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 



Y 2 



