F. A. Potts 
47 
so noticeably to receive it. There is nothing in the male to represent 
the egg-bearing swimmerets of the female : the first two abdominal 
segments only bear appendages, which are modified to form copulatory 
styles. The chelae are larger than in the female, the terminal joint 
having a swollen tumid appearance. 
A description may now be given of the deviations from the normal 
found in infected crabs. The greatest number of the male spider crabs 
with Sacculina possess fiat chelae of female type. In speaking of the 
chela as the organ which responds soonest to parasitic influence 
mention must be made of the fact that during the winter, which is the 
non-breeding season, many of the males, which are not, as far as can be 
observed, subject to the attack of any parasite, possess the flat female 
chela, a condition which is associated with a temporary suppression of 
the gonad. Both these phenomena involving chela reduction are the 
expression of a state of reproductive quiescence 1 . 
The other characters which are influenced by parasitism show no 
variation at any time from the typical form in the uninfected male. 
With regard to the shape of the abdomen more than half the infected 
crabs of male sex exhibit a condition intermediate between the narrow 
male type and the larger and broader organ of the other sex. Some 
undoubted males have a type of abdomen to be classed not as inter¬ 
mediate but wholly similar to the female. 
The assumption of abdominal swimmerets is a characteristic only 
of the more highly modified male crabs. Thus only eleven out of one 
hundred and forty examined for this particular purpose by Smith 
showed their appearance. In these few cases great variation in the 
number of appendages occurred but some exhibited the complete series 
of four pairs, and both here and wherever the swimmerets were 
developed they were seen to differ from those of the mature female 
only in their rudimentary development. 
There is of course a need of close observation in identifying the sex of 
these highly modified forms. All stages exist between the unaltered male 
and the individual which has assumed nearly all the external characters 
of the female. Such highly modified cases are in fact only to be 
distinguished at a glance from the female by the presence of recognisable 
1 The inference is that these “ suppressed ” males, after a moult shortly preceding the 
breeding season, appear with swollen chelae, by which time their testes have grown large 
and are in full reproductive activity. Though this case was not put to experimental proof 
there is no doubt that in Cambarus, a fresh-water crayfish, a form with well-marked 
secondary sex characters, passed by moulting into another form with slightly marked 
characters at the end of the breeding season (Faxon, 1885). 
