288 



CHAPTERS ON EVOLUTION. 



ingenious speculation that " each arm of the starfish essentially cor- 

 responds in its organisation with an articulated worm," is objected to 

 by some naturalists, and amongst others by Huxley, who agrees that 

 the starfish, or echinus, may have arisen from a worm-stock, but 

 argues that both the starfish and sea-urchins owe to secondary modi- 

 fication their characteristic form. Haeckel, however, is supported by 

 authority so eminent as Gegenbaur, who remarks, that " there is a 



certain amount of indepen- 

 dent organisation in each 

 arm of a starfish ; its organs 

 . . . have exactly the same 

 position as the homologous 

 organs of an Annulate worm. 

 If, then, we compare each 

 of the budding arms with 

 a worm -like organism, we 

 must regard the starfish de- 

 veloped by this process of 

 gemmation as correspond- 

 ing to a multiple of such 

 organisms ; and, further, 

 we must recognise in this 

 phenomenon the same pro- 

 cess of gemmation (or bud- 

 ding) as that which takes 

 place in other lower ani- 

 mals ] for example, in the 

 compound ascidians (or 

 sea-squirts) It is a process," says Gegenbaur, "in which several 

 separate animals are simultaneously budded off; the process does 

 not go on till these animals are completely separated, but stops in 

 such a way as to keep them connected together as an individual 

 of a higher order." We know, as just remarked, of allied cases 

 amongst the sea-squirts, where several beings are budded in star- 

 shaped fashion (Botryllus) to form a colony. And when we 

 reflect that, as every sea-beach shows, a starfish may be deprived 

 of all its arms, and as one arm (Fig. 195, 3) may not merely live an 

 independent existence, but will in time reproduce the other four, 

 Haeckel's idea that a star-fish is really a collection of worm-like 

 beings, is seen to be so far supported by comparative anatomy and 

 by the analogies of development as well. 



The list of animal classes in which a colonial constitution is 

 developed may appropriately enough be concluded with the brief 

 recital of the process whereby the Aphides, or plant-lice (Fig. 196), 

 which devastate our plants, and the bees themselves, propagate their 



FIG. 195. STARFISHES. 



