50 INSUFFICIENT KNOWLEDGE OF EXISTING FORMS. 



^0. But Fossil Remains are sometimes found, which perplex 

 the most accomplished Zoologist ; their dissimilarity to all the 

 forms of Animal structure with which lie is tami'iiar, being such 

 as to leave him very much in the dark, as to the true characters 

 and positions of the animals, of which they are tiie sole represen- 

 tatives. It is probable, however, that the progress of discovery 

 will bring to light new facts regarding their structure ; either by 

 affording more complete specimens of the remains themselves, by 

 which it may be better understood ; or by disclosing to us some 

 points in the structure or history of existing animals, which shall 

 unveil the close relationship that they may really bear, although 

 this is at present obscured by superficial differences ( 32). 

 In this manner, therefore, we may expect that many spaces in 

 our Classification will be hereafter tilled up, which at present 

 appear to be altogether blank. 



31. It is not only, however, from the incompleteness of our 

 knowledge of the various kinds of Animals, at present or for- 

 merly existing, that the foundations of a sound Zoological classi- 

 fication are as yet very imperfect ; for of a large part of those, 

 with whose external forms the Naturalist is familiar, the internal 

 structure has been but very imperfectly, or not at all, investi- 

 gated. Hence, a great part of their arrangement into groups is 

 founded upon a small number of characters only ; and not at all 

 upon i\\&l general comparison of them, which alone can securely 

 indicate their real relationship. There is, consequently, a field 

 for investigation, in this department alone, which may occupy 

 an almost unlimited number of inquirers for a very long time ; 

 and any such systematic examination, even of very common 

 animals, if prosecuted with a sufficient amount of guidance from 

 previous knowledge, would be attended with the utmost ad- 

 vantage to science. And it is not only in determining the true 

 relations or affinities of species or of groups which are known to 

 be nearly allied, that this kind of knowledge is available ; for it 

 often serves to indicate the most unexpected and beautiful analo- 

 gies, between groups far distant from each other, but occupying 

 a corresponding place in their respective classes. Thus we ^liall 



