594 
GEOFFREY SMEPH. 
extent of the material upon which my conclusions are based, 
but also the invariable certainty and regularity of the effect 
observed. 
'File sexes of normal uninfected Inachus mauritanicus 
differ in that the adult male (PI. 30, figs. 1 and 2) possesses 
greatly elongated and swollen chelae, while the abdomen is 
small in size, is carried flatly opposed to the thorax, and is 
furnished with only two pairs of appendages — viz. a large 
pair of stout copulatory styles and a greatly reduced pair of 
appendages behind them. The adult female (PI. 30, 
figs. 10 and 11) has small, slender chelae and an exceedingly 
broad, trough-shaped abdomen which is furnished with four 
pairs of bi-ramous appendages. These appendages are clothed 
with long hairs, some of which are used for attaching the 
eggs. 
The sexual difference in the chelae is not developed until 
maturity, but the differences in the abdomen are marked 
soon after the Megalopa larval stage and long before maturity. 
The female, however, ait first goes through a stage in which 
the abdomen is comparatively small and flat, and the 
appendages are short and rod-like without the filamentous 
haiirs characteristic of the adult (PI. 30, figs. 13 and 14). 
The males infected with Sacculina show every degree of 
modification towards the female type (PI. 30, figs. 3 to 9). 
In some the only change to be observed externally is the 
reduction in size of the chelae, and perhaps a slightly tapering 
form induced on the usually stout and blunt copulatory style 
(PI. 30, fig. 5). In others the abdomen is somewhat 
broadened (PI. 30, figs. 3 and 4), and in a further stage 
the abdomen is distinctly broadened and somewhat trough- 
shaped, while perhaps one or two additional appendages are 
developed in a rudimentary condition behind the reduced 
copulatory styles (PI. 30, fig. 6). If such forms are carefully 
dissected the gonad is observed to be greatly shrivelled, but 
it can still be clearly recognised as a testis, while a few 
clumps of spermatozoa may be found in the vasa deferentia. 
Finally we obtain forms (PI. 30, figs. 7, 8 and 9), usually 
