ClIAUACTlUuS OF ADAl'TATION. 



establish the aliinifcies or the genealogy of an animah Since 

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



Fig. 2.^Piag-mm of tlie Innt^ and circnlat.ion of Bir(/u.t hiiro, the Palm Crab. T- The 

 Iung--Tes3e]3 indicateil ^Yitl^i^ tlie outline of the animal— a,, n^, (T'3,t]ie three upiier affer- 

 ent vessels (veins) ; e I, ttie efferent vessel (artery) ; e h'-, section of the opening of the 

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

 lettered as above— 6/', gills or brand ii;i/ ; ",, the lower afferent vessel (vein) ; 1, the lung 

 cavity, showing the puhnonary villi (tuft-) on the inner surface of the \va]l. 



fact been the method of moi.lern zoology ; and J do not fear 

 contradiction when I say th:it we have already made consider- 

 able advances in the art of discriminating between those typical 



