GENESIS. 275 



while other branches are still producing only leaf-bearing 

 axes; and in the successive generations of Aphides a parallel 

 fact has been observed. Lastly has to be set down 



that kind of heterogenesis in which, along with gamogenesis, 

 there occurs a form of agamogenesis exactly like it, save in 

 the absence of fecundation. This is called true partheno- 

 genesis — reproduction carried on by virgin mothers which are 

 in all respects like other mothers. Among silk-worm-moths 

 this parthenogenesis is exceptional rather than ordinary. 

 Usually the eggs of these insects are fertilized; but if they 

 are not they are still laid, and some of them produce larvae. 

 In certain Lcpidoptera, however, of the groups Psychidce and 

 Tineidce, parthenogenesis appears to be a normal process — 

 indeed, so far as is known, the only process; for of some 

 species the males have never been found. 



A general conception of the relations among the different 

 modes of Genesis, thus briefly described, will be best given 

 by the following tabular statement. 



f Oviparous 

 j or 

 ' Homogenesis, which is usually Gamogenesis ^ Ovo-viviparous 

 .2 or 



2 [ Viviparous 



w -, or 



§ f Gamogenesis 



O J alternating 



Heterogenesis, which is j with C Parthenogenesis 



[ Agamogenesis < or f Internal 



[ Metagenesis < or 



[ External 



This, like all other classifications of such phenomena, pre- 

 sents anomalies. It may be justly objected that the pro- 

 cesses here grouped under the head agamogenesis, are the 

 same as those before grouped under the head of discontinuous 

 development (§ 50) : thus making development and genesis 

 partially coincident. Doubtless it seems awkward that what 

 are from one point of view considered as structural changes 

 are from another point of view considered as modes of multi- 



