CHARACTERS OF ADAPTATION. 



establish the affinities or the genealogy of an animal. Since 

 the first appeai-ance of Darwin's well-known work, this has in 



FIG. 2. Diagram of the Inngs and circulation of Birgus Jatro, the Palm Crab. I. The 

 Inng- vessels indicated within the outline of the animal <i,, n^. a,, the three upper affer- 

 ent vessels (veins) ; e I, the efferent vessel (artery) : e b*, section of the opening of the 

 arterial gill-vessel ; h, heart ; h b, jiericardium. II. Diagram of section of the same, 

 lettered as above 6/ - ,gills or branchiie; f 4 , the lower afferent vessel (vein) ; 7, the lung 

 cavity, showing the pulmonary villi (tufts) on the inner surface of the wall. 



fact been the method of modem zoology ; and I do not fear 

 contradiction when I say that we have already made consider- 

 able advances in the art of discriminating between those typical 



