298 
MR. W. BATESON ON SOME VARIATIONS OP CARDIUM EDULE 
is offered by the fatina of isolated lakes of various composition and of different degrees 
of salinity, aad the following observations were made in accordance with this view. 
They are chiefly interesting owing to the great scarcity of any systematic observations 
of the relations between variation and the condition of life and to the rare occurrence 
of opportunities for investigating them. 
While it has been held by some persons that the conditions of life are without 
definite effect in producing variations in animals, others, on the contrary, regard their 
production as an obvious consequence. The result of my investigations is to show 
that the wliole relation between variation and conditions is much more complicated 
than it wouldj^e in accordance with either of these views ; and that, while one animal 
may be profoundly and uniformly modified in every case by a certain change of 
conditions, yet these same changes produce no palpable effect on an allied animal of a 
different sort. For example, particulars will be given of the constant modification of 
Cardium edule consequent upon the drying up of the lakes in which they were, while 
Dreissena iiolymorplia and Hydrohia uIvcb do not appear to have been affected. It 
may be here remarked that the general variability of a form, as Dreissena polymorpha, 
does not appear to predispose it to assume a new form for a given change of condition. 
In view of the fact that definite variations have been shown to be produced in 
Cardium edule by change in the composition of the water, it next becomes desirable 
to know to what extent these changes would be maintained if the conditions were 
altered back again to their original state. Upon this point I have no evidence ; but 
that the animals would, if they lived and propagated, ultimately regain their former 
structure appears probable ; for, since it can be shown that certain variations are 
constantly produced by water of certain constitution, it practically follows that the 
maintenance of these variations depends also on the same cause. It would, however, 
be of the greatest interest to ascertain the length of time and the number of genera¬ 
tions necessary to effect these changes. 
The specimens forming the subject of this paper were collected in the district of the 
Aral Sea and in Egypt. 
In 1886 and 1887 I made a journey to some of the lakes of Western Central Asia, 
for the purpose of making observations on their fauna. As the waters of these lakes 
are of very various composition, being salt, alkaline, bitter, or fresh in differing degrees, 
I looked forward to an opportunity of investigating the question whether these diverse 
environmental conditions produce any correlated changes in the structure of the 
animals which are exposed to them. The collections made with this object consist 
chiefly of Crustacea, of which an account will be published hereafter. 
In the course of the journey thus undertaken, I visited the northern shores 
of the Aral Sea and the sandy region called lyara-IUun, over a part of wdiich, at least, 
the Aral Sea formerly extended, as is shown by the quantities of shells of the 
Aral Sea Cockle which are strewn on it. The area from which the Aral Sea has thus 
receded is not a level tract, but contains three considerable depressions, called 
