112 A HISTORY OF RECENT CRUSTACEA 
are dispersed upon the shore, but that in winter the females 
collect on the deeper rocky ground in particular spots in a 
great crowd, and pile themselves up in such numbers that 
they form a sort of mound, which from the depth of eighty 
to a hundred feet ascends until the glimmer of it can be 
seen at the surface of the water, and that then the Istrian 
fishermen go out with two, four, or six boats, surround this 
living tower with their nets as easily as possible, and so 
make a speedy capture. Professor Stalio, in 1877, en- 
dorses this wonderful tale, except that in his account the 
boats employed are only two or four, and the instinct which 
leads these creatures to cling together and climb up one on 
another’s back only produces a great pile of several feet in 
height. Yet anything much less than Olivi’s submarine 
mountain of crabs would scarcely be visible from the sur- 
face at the depths which he mentions. 
The Mediterranean possesses another closely allied spe- 
cies, Muia verrucosa, Milne-Edwards, smaller in size, and 
covered with warts or tubercles, instead of spines or prickles. 
This little crab led the way in quite recent years to some 
observations that throw a new light upon the mental powers 
of the Crustacea. 
A great many of the Oxyrrhyncha have at all periods 
excited the surprise of collectors, when dealing for the 
first time with living specimens, by their often extreme un- 
tidiness. They are overgrown with alge and ever so many 
kinds of sedentary animals. They are undoubtedly them- 
selves slow-moving creatures, and it was not unnaturally 
supposed that these colonies with which they were encum- 
bered and disfigured were at once a proof and a result of 
their extreme sluggishness. Dr. Graeffe had once occasion 
to carry into the aquarium at Trieste a specimen of Maia 
verrucosa which had been stripped of most of its vegetable 
costume. He happened to place it in the same vessel with 
a large mass of the polyp known as Dead Man’s Fingers. 
The next day, to his astonishment, he found the whole 
back of the Spider-crab covered with pieces which had 
evidently been snicked out of the Alcyonium. ‘To make 
sure, he kept watch, and at length had the sweet satis- 
