Chap. XIV.] ORaANlC BEINGS. 231 



>vny, in finding the relations between one group and 

 another, we summarily reject analogical or adaptive 

 characters, and yet use these same characters within 

 the limits of the same group. We can clearly see 

 how it is that all living and extinct forms can be 

 grouped together within a few great classes; and how 

 the several members of each class are connected to- 

 gether by the most complex and radiating lines of 

 affinities. We shall never, probably, disentangle the 

 inextricable web of the affinities between the members 

 of any one class; but when we have a distinct object 

 in view, and do not look to some unknown plan of crea- 

 tion, we may hope to make sure but slow pro- 

 gress. 



Professor Hackel in his ' Generelle Morphologic ' 

 and in other works, has recently brought his great 

 knowledge and abilities to bear on what he calls phylo- 

 geny, or the lines of descent of all organic beings. In 

 drawing up the several series he trusts chiefly to em- 

 bryological characters, but receives aid from homologous 

 and rudimentary organs, as well as from the successive 

 periods at which the various forms of life are believed 

 to have first appeared in our geological formations. He 

 has thus boldly made a great beginning, and shows us 

 how classification will in the future be treated. 



Morphology. 



We have seen that the members of the same class, 

 independently of their habits of life, resemble each other 

 in the general plan of their organisation. This resem- 

 blance is often expressed by the term " unity of type; " 

 or by saying that the several parts and organs in the 

 different species of the class are homologous. The whole 



