58 A HISTOHY OF EECENT CKUSTACEA 



discovered their haunts.' Mr. Couch found that thig 

 referred to the mating time, which occurs just after the 

 female has cast her coat, her new shell being still soft. 

 It is easy to understand why the exuviation of the male 

 takes place at a different period, as otherwise the pair 

 would be defenceless together. Of this Cancer ^jaguriis, 

 Linn., small specimens are often sheltered in considerable 

 numbers in cavities wrought in the vast masses of the 

 sand-tubes of the marine worm Sahellaria alveolata. 



Cancer irroratus, Say, is the commonest species of the 

 genus in America. It is exceedingly like the European 

 species, but smaller, with the chelipeds less bulky, and dis- 

 tinguished by a strong tooth on the fifth joint. It is said 

 to be common under the large rocks near low-water mark, 

 often lying nearly buried in the sand and gravel beneath 

 them. It is also frequent on sandy shores, and occurs in 

 the tidal pools, where, according to Professor Verrill, ' the 

 comical combats of the males may sometimes be witnessed.' 

 Miss J. M. Arms founds upon it the following description 

 of a crab's method of walking : — 



' The legs of one side are used to push with, and those 

 of the other to pull with, when the crab is in motion. 

 Those of the same side do not, however, all move together, 

 but alternately, so that there is no halting in their gait ; 

 some of the legs are always in the act of taking new steps, 

 and by shoving and pulling in unison a continuous motion 

 is kept up. This crawling by means of jointed appen- 

 dages can be imitated after having once seen a live crab. 

 Cross the two wrists side by side, placing the fingers down 

 on a level table ; bind the wrists by an elastic band, hold 

 them well up from the table, so as to show the fingers. 

 Then let one set crawl while the other pushes, so as to 

 keep up a continuous motion side wise without assistance 

 from the arms. The terminal sections of the legs show 

 wear only on the points where these are inserted in the 

 ground.' 



It will subsequently be seen that there are some crabs 

 which are by no means limited to the slow progression 

 denoted by the word crawling. 



