24 THE SHELL-FISH OF THE COAST, 
which, in the living condition of the organism, the 
tiny white polyps, with their circle of tentacles, 
may be seen to rise to a height of perhaps a 
quarter inch or so. Between these tentacular 
polyps again, which are strictly those elements 
of the compound organism which secure nutrition 
to the colony at large, may be found at times a 
number of smaller bodies, without tentacles, which 
give origin to, and carry, the egg-capsules, in each 
of which there are from one to five eggs. Thus 
does this diminutive colony live in concert, dif- 
ferent parts administering to the different wants of 
the assembled multitude. Most of the crusts of the 
Hydractinia echinata, for so the polyp is called, are 
found on the hermit-inhabited shells, but naturally 
where these have been exposed for too long a time 
to the dry atmosphere only the crust remains. 
Along with the dog-whelks, we find many of the 
tide-waters pools inhabited by a number of small 
round-mouthed shells, known as periwinkles or 
Littorinas, a northern species of which 
(Littorina litorea), inhabiting both the 
American and European coasts, is the 
common periwinkle of the English 
markets. These interesting creatures, 
of which there are three species* on 
the New Jersey coast, are truly marine 
in habit, but still prefer for their habi- 
tations localities that are only partially 
PERIWINKLE (Lit- 
torina trrorata), 
* Since the above was written Littorina litorea has been found 
at Atlantic City ; it is a much less elevated shell than the common 
large periwinkle of our coast (L. irrorata). 
