34 ZOOLOGICAL PHILOSOPHY 



Finally, it was through the study of affinities that I succeeded in 

 effecting a number of necessary alterations even in the classification 

 of molluscs, and that I recognised that the pteropods, which are closely 

 aUied to but distinct from the gastropods, should not be placed 

 between the gastropods and the cephalapods, but between the ace- 

 phalic molluscs and the gastropods ; since these pteropods, hke all 

 acephaUc animals, have no eyes and are almost without a head, not 

 even excepting Hyalea. (F. the special classification of molluscs 

 in Chap. VIII., at the end of Part I.) 



When the study of affinities among the different known families 

 of plants has made us better acquainted with the rank held by each 

 in the general series, then the classification of these living bodies 

 will leave nothing more to arbitrary judgment, but will come more 

 closely into conformity with the actual order of nature. 



The study of the affinities among observed objects is thus clearly 

 so important that it should now be regarded as the chief instrument 

 for the progress of natural science. 



