96 A HISTOKY OF RECENT CRUSTACEA 



The detached figures show the chelae of the young male 

 and the female, and the pleon respectively of male and 

 female. By the Japanese this species is called the moun- 

 tain savage or the hairy crab. It occupies brackish 

 waters, passing from them into fresh-water streams, by 

 means of which it ascends the mountains, where it is often 

 observed on dry land. 



Vwruna, Milne-Edwards, 1830, has the single species 

 Varuna litterata (Fabricius), common in the Indo-Pacific 

 region, and attracting attention by the marking on the 

 carapace to which the specific name refers. The capital 

 letter H is here considered to be formed with more than 

 usual distinctness by the longitudinal grooves that sepa- 

 rate the lateral from the median regions, and the trans- 

 verse groove which appears to form the upper boundary 

 of the cardiac region. 



Sesarma, Say, 1818, includes a large number of species 

 found in the shallow waters of all the warm regions of the 

 globe. In this genus the ' front ' is broad ; the third 

 maxillipeds, when closed, still leave open a lozenge-shaped 

 space, and have the large fourth joint traversed by a ridge 

 from the front inner angle to the outer angle behind ; the 

 pterygostomian regions have a granular or reticulated sur- 

 face, which in general is divided into little squares of 

 extreme regularity. 



Reference has been already made to Fritz Miiller's in- 

 vestigation of the breathing arrangements in land-crabs. 

 He was anxious to put the theory of evolution to a test. 

 The resemblances which prevail among all crabs point, on 

 that theory, to their derivation from a common ancestral 

 form, but the differences which prevail in the numerous 

 genei'a of land-crabs point to a divergence that must have 

 begun long before they assumed terrestrial habits. That, 

 at least, is what Fritz Miiller assumes, and few evolution- 

 ists will be inclined to deny it. If, then, several different 

 forms of water-breathers at various times and places have 

 independently developed into air-breathers, it is unlikely 

 that the necessary changes will all be of the same pattern. 

 It is so unlikely that, had it proved to be the case, Fritz 



