278 
GEOFFREY SMITH. 
prolonged period entirely inhibits moulting in Carcinus, but 
does not appreciably reduce the amount of glycogen in the 
liver. 
The influence of Sacculina upon moulting and the de- 
position of glycogen in Carcinus is very definite and 
of great interest. After the small Sacculina lias once 
penetrated to the exterior of its host, the latter never 
moults again so long as the Sacculina remains on it, and 
even after the Sacculina has dropped off moulting does 
not occur for a very long poriod, and in most cases not at all. 
'Idle reason of this inhibition of growth and moulting can be 
clearly traced to the inability of the parasitised crab to lay 
up sufficient stores of glycogen under the skin, as, if the skin 
underlying the hard shell of a parasitised crab be examined, 
it is found that a very small amount of glycogen is present 
compared to the condition found in a normal healthy crab 
with a hard shell. This cannot be ascribed to a general state 
of bad nutrition, as crabs with Sacculina on them always 
contain an abundant supply of fat in the liver. It seems, on 
tlie contrary, that the effect of the Sacculina is to stimulate 
tlie fatty function of the liver and to depress the glycogenic 
function, and when we come to consider the quantitative 
determinations of fat and glycogen in the liver, we shall find 
that this is indeed the true explanation. It is, however, a 
remarkable fact, first noticed by F. A. Potts (5j, that Pelto- 
gaster, so far from inhibiting moulting in its host, the hermit 
crab, actually stimulates it to moult more frequently than 
usual — an effect which is the exact opposite of what occurs in 
the case of Sacculina and its hosts. 
This striking antagonism in results between the two cases 
evidently calls for some explanation, and the obvious sugges- 
tion to account for it is that the Sacculina and Peltogaster 
roots respectively differ in their activities in some way. It is 
clear, for instance, that if the Sacculina roots could be shown 
to contain no glycogen, but only fat, while the Peltogaster 
roots could be proved to store glycogen in considerable 
quantities in addition to fat, then we could readily understand 
