488 LAWS OP MULTIPLICATION. 



germ-producing organs and their contents, eventually 

 acquire a total bulk many times that of all the other organs 

 put together. Numerous species of this type and habit, 

 repeat this relation between a life of inaction with high 

 feeding, and an enormous rate of genesis. Parasites belong- 

 ing to another great division of the animal kingdom, the 

 Platyhelminthes, supply an example of an epizoon in which 

 the rate of multiplication is made great not so much by 

 immense development of the egg-producing organs as by 

 the rapidity with which generations succeed one another a 

 rapidity such that each generation partially develops the 

 next before it is itself anything like ready for independent 

 life. This is the Gyrodactylus elegans, of which it is said 

 that " its most remarkable feature is that it is viviparous, 

 and its embryos before they leave the body of their mother 

 have already developed their embryos inside them; and the 

 latter may contain their embryos, so that four generations 

 may be included under the cuticle of the sexually mature 

 animal." * 



Entozoa yield us many examples of this causal relation, 

 raised to a still higher degree. The Gordius, or Hair-worm, 

 is a creature which, finding its way when young into the 

 body of an insect which is afterwards swallowed by a fish, 

 there grows rapidly, and then emerging to breed, lays as 

 many as 8,000,000 eggs in less than a day. Similarly with 

 those larger types infesting the higher animals. It has been 

 calculated by Dr. Eschricht, as quoted by Professor Owen, 

 that there are "64,000,000 of ova in the mature female 

 Ascaris lumbricoides." Very many of the Entozoa belong to 

 the Platyhelminthes, and among them occur examples of fer- 

 tility caused not only by great numbers of ova, but by rapid 

 succession of partially-developed individuals and also exam- 

 ples of fertility caused by production of ova almost exceeding 

 numeration. Among the first the Liver-fluke may be named. 

 Of the half-million eggs it produces each yields a free-swim- 

 * Shipley, Zoology of Irivertebrata, p. 112. 



