CHARACTEKS OF ADAPTATION. 5 



establish the affinities or the genealogy of an animal. SinQe 

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



Fig. 2. — Diagram of the lungs' and circulation of Birgus latro, the Palm Crab. I. The 

 lung- vessels indicated within the outline of the animal— a,, a„, cfg, the three upper affer- 

 ent vessels (veins) ; e I, the efferent vessel (artery) : e &'■, section of the opening of the 

 arterial gill-vessel ; A, heart ; h 5, pericardium. II. Diagram of section of the same, 

 lettered as above— &/% gills or branchiaa; n^, the lower afferent vessel (vein) ; i, the lung 

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



fact been the method of modern 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 



