22, A HISTORY OF RECENT CRUSTACEA 
head and other parts of the whale while the monster is still 
alive. On the other hand, whales and seals, and fishes 
large and small, swallow down the Crustacea in a truly 
wholesale manner, and so prevent these prodigiously 
prolific animals from producing a complete block in the 
cooler parts of the ocean. Independently of this interest- 
ing exchange of courtesies, which consists in alternately 
eating and being eaten, there is another kind of associa- 
tion between crustaceans and other animals, known as 
commensalism. In this the one creature lives, not at the 
expense of the other, but merely in companionship with 
it. Thus, on the common starfish there is found a thread- 
like fiibate species of the Caprellidee. Though the star- 
fish is very frequéntly to be met with on the shores, its 
companion Pariambus typicus (Kréyer)' is only seen on 
dredged specimens, so that apparently this tiny animal 
has the sense to disengage itself when its host is being 
driven into an unsuitable or dangerous position. Some of 
the Amphipoda Hyperidea are very frequently to be found 
upon jelly-tishes. One of the Gammaridea, Jscea Montagui, 
Milne-Edwards, appears never to have been found except 
upon the Spinous Spider Crab, Maia squinado, for clinging 
to which its feet, with their serrate widened extremities, 
are peculiarly adapted. A French zoologist, M. Edouard 
Chevreux, some five or six years ago, was searching this 
interesting crab for its already well-known commensal, 
when to his surprise, among the alge and hydrozoa, with 
which the carapace is usually decked, he found not only 
the species he was in search of, but no less than twenty- 
two other species of Amphipoda into the bargain. Maia 
squinado is not found far to the northward. On the other 
hand a very distinct crab, but with some external re- 
semblance to it, Lithedes miaia, is not found far to the 
southward. Such facts of distribution are often of scien- 
tific importance. For instance, with regard to the com- 
paratively narrow strip of land which separates North 
from South America, the geologist will desire to know how 
far the crustacean fauna of the sea on one side of the 
‘Formerly Podalirius typicus. 
