146 



The Naturalist. 



" alternation of generations," A produces B, never A ; the latter is 

 always the offspring of B : but with the DapJmice it is A only, all 

 through the series. 



The resemblance to the reproduction in Hymenoptera, which some 

 writers detect, is equally fanciful. The males of the hive bee {Apis 

 mellifica), always arise from the unimpregnated ova, and those eggs 

 which, if impregnated, would have produced females, will, if no 

 spermatozoa are present, give birth to males. But with Z)aj!;7m'ce 

 fertilization stands in no relation to the evolution of sexual forms. 



Even to describe this mode of reproduction as " parthenogenesis," 

 not only must we abandon the vital principle of the theory, viz : — that 

 virgin products exhaust the spermatic virtue ; but we have also to 

 depart from the typical example. The winged and perfect ^^/m produces 

 wingless hexapod larvae, and these, in the absence of males, again produce 

 their like through numerous 'generations, all summer; the last brood gives 

 rise to perfect winged insects, true male and female, the fertilized ova 

 of which lie over winter, and in spring develop wingless larvse. But 

 the two kinds of ova of Daplmioe are evolved synchronously, and the 

 offspring always resemble their progenitors. The nearest analogy to 

 Daphniadie is among those Rotifera [Asplanchia, &c.) which hatch 

 their agamic ova, and also lay " winter eggs," for the development of 

 which the male element is requisite. 



Huxley (5) defines an individual as the total product of a fertilized 

 ovum. But this conclusion is not without its difficulties. If it be 

 true, there is no such thing as a male individual Baphiia^ Apis, or 

 Aphis, no more than is a tree raised from a cutting an individual 

 tree. " Every organism springs from an egg" is a well-known axiom. 

 But what is an egg ? Take a Hydra viridls, on the outer surface 

 of which three little prominences have arisen. One shall enlarge, 

 develop tentacles, and float away to reproduce its kind. The other two 

 will also expand, one will contain a nucleated the other a non- 

 nucleated cell ; when freed, the latter will be absorbed by the former, 

 and another polypite will arise, exactly resembling the product of the 

 first prominence, and inheriting the same vital powers. We call one 

 a bud, the other an ovum. Wherein lies the difference ; is not every 

 ovum essentially a bud ? Doubtless. But buds are a stage of 

 development, not of reproduction. They are of two kinds, barren and 

 fertile. The agamic ova of the Daphnia are fertile buds ; the ephippial 

 eggs are barren buds, the impregnation of which is the first stage of 

 reproduction. 



(5) Annals of Natural History, June, 1852. 



