STUDIES IN ANIMAL LIFE. 31 



with other organs which their parent was without. 

 To look at them you would as soon suspect a shrimp 

 to be the progeny of an oyster, as these to be the 

 progeny of the sac-animal. And what makes the 

 paradox more paradoxical is, that not only are the 

 Cercarice unlike their parent, but their parent was 

 equally unlike its parent, the embryo of Monosto- 

 mum (compare Fig. 4). However, if we pursue this 

 family history, we shall find the genealogy rights 

 itself at last, and that this Cercaria will develop in 

 the body of some bird into a Monostomum mutabile 

 like its ancestor. Thus the worm produces an an- 

 imalcule, which produces a sac-animal, which pro- 

 duces a Cercaria, which becomes a worm exactly 

 resembling its great-grandfather. 



One peculiarity in this history is, that while the 

 Mbnostomum produces its young in the usual way, 

 the two intermediate forms are produced by a process 

 of budding analogous to that observed in plants. 

 Plants, as you know, are reproduced in two ways 

 -from the seed and from the bud. For seed- 

 reproduction peculiar organs are necessary; for 

 bud-reproduction there is no such differentiation 

 needed: it is simply an outgrowth. The same is 

 true of many animals; they also bud like plants, 

 and produce seeds (eggs) like plants. I have else- 

 where argued that the two processes are essentially 

 identical, and that both are but special forms of 

 growth.* Not, however, to discuss so abstruse a 



* Seaside Studies, p. 308 et sq. 



