LIMA HIANS AND ITS MODE OF LIFE. 919 
There are, however, two closely allied types which have not 
this thick shell, and have to make shifts to protect themselves in 
other ways. It is this very weakness, however, which has led to 
their higher development as compared with that of their more 
sluggish relative, They may be described as reformed oysters, for 
their modifications, we have reason to believe, are of a secondary 
origin. The reform has taken place in two directions, and it is 
with one of these that we are specially concerned. 
The only points of direct communication between the siti 
and the outside world are the edges of the mantle which secrete 
the shell, and the foot. It is in these that the advance in organ- 
isation shows itself. 
Pecten, our common Scallop, is an animal of comparatively 
active habits. It can suddenly close its shell, driving out the 
water so forcibly as to give the body an impetus in the opposite 
direction, so that, unlike the Oyster, it has some power of loco- 
motion. Besides, the edge of the mantle is fringed with a series 
of eye-spots sensitive to the lightest shadow, and thus capable of 
giving timely warning of the approach of danger. 
The other direction in which specialisation is exhibited is in 
Lima, another genus of the same family. . There is also here a 
comparatively thin shell, but the shells cannot be securely closed 
as in Pecten, and a large gap is left even when the valves are 
closely appressed. The animal, however, protects itself in another 
way. It has also, though not eyes, elaborate sensory organs, fitted 
to its special mode of life. 
Having made ourselves acquainted with the family connections, 
or to use Haeckel’s useful word, the ‘“ palingenetic” character of 
Lima, we are now in a position to investigate the personal char- 
acteristics by which it is adapted to its own peculiar mode of life 
—the ceenogenetic or more recently acquired chamacters. 
Various observers have devoted attention to the habits of Zima 
hians, the animal which we are about to examine, as it affords 
special facilities for observation, being easily kept in eaptivity. 
We owe many valuable observations on the living animal to 
Robertson, Norman, Landsborough, and others. More minute 
histological work has been done by Rawitz. The aim of the pre- 
sent paper is, by combining these observations on the living and 
dead animal, and by recording some new observations, to give a 
- general sketch of the animal and its mode of life. 
