STUDIES IN THE EXPERIMENTAL ANALYSIS OF SEX. 285 - 
crabs have a more constantly liig-h percentage of fat in the 
liver than normal males, and this is completely l)orne out by 
the' quantitative results. 
The table shows that, both in respect of glycogen and fat,, 
the infected crabs have a more equable and dehuite sup])ly 
of these reserve materials in the liver, that under ordinary 
conditions of feeding they do not show the same degree of 
variation and fluctuation in respect to the storage of these 
substances as the normal males do. Xow the normal males 
are in various conditions according to the period of the 
life-cycle they happen to have reached — e. g. some are 
reproducing, others- are growing actively and about to moult,, 
etc. — whereas the infected individuals are dominated by one 
constant condition, the presence of a parasite which is 
demanding a certain kind of food from its host, principally 
of a fatty nature. This constant demand leads to a stereo- 
typed and constant type of metabolism, which is principally 
characterised by a constantly high elaboration and storage of 
fat in the liver. It would seem that a normal, though not 
excessive, supply of glycogen is also present in the livers of 
infected crabs, but in the case of Carcinus at any rate there 
is no periodical heaping’ up of glycogen in the liver or skin 
for the purpose of a moult, which, in fact, does not occur. 
From Pott’s observations on Pagurids infected with Pelto- 
gaster it might be surmised that the glycogenic function of the 
liver is in some way stimulated, leading to frequent monlts. 
Exactly what happens in this case is not really known, but, 
as has been pointed out, it is at any rate doubtful if the 
infected Pagurids actually grow any faster than normal 
individuals, since the infected forms are by no means on 
the average larger than the normal, which tliev certainlv 
should be if their frequent moults resulted each time in an 
increase in size. 
We know from other cases that growth and moulting av/e 
not always coincident phenomena in Crustacea. Tinas, in 
certain Amphipods the recent work of Mrs. Sextom and Mrs. 
Matthews ( 11 ) has shown that the adult femalo..- moults far more- 
