98 A HISTORY OF RECENT CRUSTACEA 
discovered their haunts.’ Mr. Couch found that this 
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 paqurus, 
Linn., small specimens are often sheltered in considerable 
numbers in cavities wrought in the vast masses ef the 
sand-tubes of the marine worm Satellaria 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 sidewise 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. 
