96 A HISTORY OF RECENT CRUSTACEA 
The detached figures show the chele 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. 
Varuna, 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 
genera 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, 
Xt is so unlikely that, had it proved to be the case, Fritz 
