THE LAW OF LIKENESS, AND ITS WORKING. 207 



of nature, and dire confusion becomes the order of the day. 

 As will be hereafter shown, however, whilst the law of 

 variation does undoubtedly operate, and that to a very great 

 extent, amongst living beings, other and compensating con- 

 ditions are brought to light by the careful study of develop- 

 ment at large ; and the old law of like producing like may 

 be seen, after all, to constitute the guiding principle of 

 nature at large. As a study of high interest, and one the 

 elements of which are afforded by our observation of the 

 everyday world, the investigation of the law of likeness may 

 be safely commended to the seeking 

 mind. And in the brief study of 

 this law and its operations we may 

 firstly glance at some instances of 

 development by way of illustration, 

 and thereafter try to discern the 

 meaning and causes of similitude 

 or heredity. ' ' Rassemblons desfaits 

 pour nous donncr des idees" says 

 Buffon, and the advice is eminently 

 appropriate to those who purpose 

 to enter upon a popular study of an 

 important natural law. 



One of the simplest instances 

 of development, in which the young 

 are not only transformed directly 

 into the likeness of the parent, but 

 represent in themselves essential 

 parts of the parent-body, is illus- 

 trated by the case of the little worms 

 known to the naturalist as Naidides, 

 and familiar to all as inhabitants of 

 our ditches, and as occurring in 

 damp mud and similar situations. If 

 a nai's (Fig. 27) be chopped into a number of small pieces, 

 each piece will in time develop a head and tail and become a 

 perfect worm, differing in no respect, save in that of size, 



FIG. 27. A nals, or fresh-water 

 worm, producing a new indi- 

 vidual by budding. 



