THE BEGINNINGS OF LIFE. 571 



The analogy is, however, rendered all the more striking, 

 when we find that the forms of Medusae and Disto- 

 mata which undergo the exceptional direct process 

 of development are all of them notable for the very 

 large size of their eggs, whilst all those which develop 

 indirectly, through intermediate forms, invariably start 

 from much smaller eggs. It is difficult, therefore, to 

 avoid the conclusion that these previously unexplained 

 differences in the modes of origin of Medusae and 

 other organisms amongst which c alternate generation ' 

 prevails, are probably referrible to some such dif- 

 ferences as are now seen to obtain amongst Rotifers 

 and other forms which are producible by a direct or 

 an indirect origin from a transforming vegetal vesicle 

 according as it happens to be large or small. 



Variations and Transmutations of Species. 



Facts of the kind to which we have just been referring, 

 as well as multitudes of others, seem to show in the 

 clearest manner possible, how strictly the Ephemero- 

 morphs are comparable with Crystals. Their forms and 

 structures seem to be as plainly the result of the organic 

 polarities of the molecules entering into their com- 

 position, as the forms of crystals are due to the 

 polarities of their constituent molecules. There is an 

 infinitely greater diversity amongst the ephemero- 

 morphs, it is true, on account of the extreme com- 

 plexity of the different kinds of living matter, and of 



