Asymmetry , Effect of Parasites. *23 
of about 4| inches long, obtained on 16th September, 1901. Wall- 
Between that date and 31st July, 1909, when the lobster died, it ^ ses -, 0 
moulted seven times and grew to a length of 9 inches. 
Asymmetry. — A point on which information is often asked, 
the unlikeness in size and shape of the great claws of the Lobster 
and other Crustacea, is illustrated by specimens in Wall-case No. 1. 
In the preparations of the male and female Lobster (Fig. 5), for 
instance, or in the pair of claws from a very large Lobster in the 
lower part of the case, it will be seen that one of the claws is 
more massive than the other and that the fingers are armed with 
blunt knobs. It is, in fact, used for crushing the shells of animals 
on which the Lobster may be feeding, and is known as the 
“ crushing- claw.” The other is more hghtly built, with sharp saw- 
like edges to the fingers, and is known as the “ cutting-claw.” 
There is no rule as to the side of the body on which either form 
of claw is found, “right-handed” and “left-handed” specimens 
being about equally common. In others of the higher Crustacea 
the disparity in size of the two claws is much greater than in the 
case of the Lobster. This is shown by the claws of the large 
Tasmanian Crab (Pseudocar cinus gig as ) , of which a pair is 
exhibited in the lower part of Wall-case No. 1, and other examples 
will be found in the table-cases. In some crabs the larger claw 
is more or less constantly on the same side of the body ; that 
is to say, right-handed (or, more rarely, left-handed) individuals 
predominate. 
Occasionally, in the Lobster, specimens with similar claws 
occur. Most commonly, in these, both claws are of the cutting 
type, but, very rarely, specimens like that shown in the lower 
part of Wall-case No. 1, are found in which both claws are of the 
crushing type. The mode of production of such abnormalities is 
not fully understood, but it seems probable that in most cases it is 
associated with the regeneration of limbs removed by accident or 
thrown off after injury. 
MODIFICATIONS CAUSED BY PABASITES. 
A series of specimens, exhibited in Wall-case No. 2, illustrate the 
changes of structure produced in certain crabs which are infested 
by the degenerate Crustacean parasite Sacculina. It is a curious 
and significant fact that these changes affect almost exclusively 
