226 LEISURE-TIME STUDIES. 



imagination to conceive. The particles of vaccine lymph 

 diffused through the body by the lancet of the vaccinator, 

 are much more minute than the smallest cells ; yet, judged 

 by the standard of development and by the effects of 

 their multiplication in our frames, their existence must be 

 regarded as anything but problematical. Then, as regards 

 numbers, the eggs of some animals exist in quantities, of 

 which, at the best, we can only form a dim and approximate 

 idea. A small parasitic worm, the Ascaris, is known to 

 produce 64,000,000 eggs, and some of the orchids will 

 produce as many seeds ; whilst the fertility of some fishes is 

 almost inconceivable. It has been objected, it is true, to 

 this conception of the manner through which the law of 

 likeness operates, that it is difficult to believe in the 

 complicated powers and tendencies of the gemmules to 

 select and carry the special qualities of the cells from which 

 they originate ; and that, in short, the conception credits the 

 gemmules with powers of too mysterious and occult a kind 

 for ordinary acceptance and belief. But in answer to this 

 objection it may be urged that the powers with which the 

 gemmules are credited are not a whit more extraordinary 

 than those possessed by cells ; or than those which nerve- 

 cells and nerve-fibres possess, for example, in forming and 

 transmitting the undetermined, mysterious nerve-force which 

 under certain conditions becomes resolved into thought and 

 mind. The mere conditions of heredity which the theory 

 explains, constitute in fact a greater draft upon scientific 

 credulity than is demanded by any conditions or ideas 

 included in the explanation itself. 



Moreover, there is hardly a condition, illustrated by the 

 examples of heredity and animal development already given, 

 which is insusceptible of explanation through the aid of this 

 theory. The cases of fission illustrated by the fresh-water 

 worms (Fig. 27), and the process of budding exemplified by 

 the zoophyte, become intelligible on the idea that a determi- 

 nation of the gemmules to the parts concerned in these 

 processes takes place, and that by their aggregation they form 



