186 PROCEEDINGS : BOSTON SOCIETY NATURAL HISTORY. 
direct effect is involved. But when shells depart strongly from the 
dextral type, an indirect influence is exerted, dependent on the fact 
that many larvae are reluctant to enter such shells. 
Effect on health .—Another influence of the shell on the growing 
larva was brought out by the experiments. Attention has already 
been called to the high mortality among Eupagurus larvae. Now 
this mortality was especially noticeable in those experiments where 
the glaucothoe were either wholly prevented from entering a shell 
(C) or only permitted to enter one after a considerable delay 
(B 2). Here it reached about sixty percent. In the “normal” 
experiments and in the less abnormal experiments of the “delay” 
series (B 1), only forty-six and thirty percent respectively of the 
glaucothoe perished before the moult to the sixth stage could be 
reached. The entrance into a shell early in the glaucothoe phase 
has then an important bearing with regard to the health of the crab. 
At first sight also this seems to be to some extent correlated 
with the form of the shell used. The glaucothoe that lived in 
straight glass tubes (D) lost thirty-nine percent of their number, a 
death rate less than that for the normally reared crabs. The crabs 
in sinistral shells, on the other hand, had a death rate as high as that 
prevailing among crabs which never obtained a shell. But of course, 
as before, this may be the result of the reluctance of glaucothoe 
to enter sinistral shells with the consequent prejudice to their health, 
rather than a direct effect of the peculiar twist of the shell. With 
my adolescent crabs the death rate among those reared with sinis¬ 
tral shells was not noticeably higher than among those reared in 
other kinds of houses. Although this is based on a smaller number 
of crabs, it would lend support to the idea that the higher death 
rate among “ sinistrally reared ” glaucothoe was indirect. A partic¬ 
ularly disastrous experiment with adolescents showed a mortality 
among larvae living in dextral, indifferent, and sinistral shells, of 
fifty-seven, fifty-two, and sixty percent, respectively. 
The absence of a habitation is invariably injurious. The mortality 
for “ naked ” adolescents in the above experiment was eighty-one 
percent. Even with wild adults death usually follows after a short 
continuance of the “naked” condition. Injury to the soft and 
defenseless abdomen is generally the immediate cause of death, but 
there are occasional indications which may point to some general 
physiological disturbance caused by the lack of a body covering. 
