SECT. XII RELATION OF APUS TO CRUSTACEA 177 



mcnt has been arrived at as to the true zoological 

 position of Limulus. Many eminent zoologists, such 

 as Van Beneden, maintain that Limulus is not a 

 Crustacean at all;^ and the able attempt of Lan- 

 kester and others to demonstrate that Limulus is 

 an Arachnid is familiar to all zoologists. 



The difficulties in the way of connecting Limulus 

 and Apus seem to be the following, (i) The limbs 

 in the two animals are differently arranged on the 

 body, besides differing in number and form. This 

 point is rightly considered of great importance, 

 because it was chiefly the close study of the limbs, 

 and of their homologies in the different Crustacea, 

 which enabled zoologists to arrange the class into 

 the natural groups of our present classification. (2) 

 Whereas the Xiphosura bear marked!}^ the character 

 of an archaic group, whose nearest allies are to be 

 sought for in the earliest geological strata, and which 

 in development pass through a so-called " Trilo- 

 bite " stage, Apus has, comparatively speaking, no 

 geological record, and is, so far as we can learn from 

 palrEontology, rather a highly specialised tertiary 

 form. (3) The young of Limulus do not pass 

 through any stages which appear to correspond with 

 the stages of Apus. Packard's attempt to discover 

 the Nauplius stage in the embryological development 

 of Limulus has met with no favour. 



We here have, as far as we can find, the chief 



^ " Les Limules ne sont pas des Crustaces — ils n'ont ricn de commun 

 avec les Phyllopodes." Journal de Zoologic, par P. Gervais, vol. i. p, 42. 

 Paris, 1872. 



N 



