Vol, VIII, No. 2.] The Freshwater Fauna of India. 51 
[N.S.] 
organized animals such as sponges in which there are no 
definite organs and the individual cells are capable of great 
modification both in structure and in function. With this 
topic I must deal very briefly. Indeed, all that I need 
say is that whereas a very slight change in environment may 
often produce a very great change of external form (and 
occasionally a less marked change of internal structure) in 
the same species,' identity of environment does not always 
produce even similarity of external form in different species. 
These facts are well illustrated by the pictures I will now 
show you. The first of these pictures (pl. II, fig. 2) is a 
photograph of three specimens of the Himalayan race of the 
widely distributed freshwater sponge Ephydatia fluviatilis. 
These specimens were all taken in shallow water in the lakes 
of Kumaon by Mr. Kemp in May, 1911. The lower figure (A) 
represents a piece of stone to which three sponges are attached. 
They have the form of flat circular films. The specimen 
marked B was attached to a slender twig and has assumed 
the form of a cockscomb, while the one marked C was growing 
on a forked twig with not very divergent branches and is 
of somewhat irregular form. These differences in external 
shape are due solely to the nature of the object to which the 
larval sponge originally affixed itself. : 
The next three pictures (pl. III) illustrate the second point 
and aie from drawings of three different species of the genus 
Spongilla, all growing on the roots of the same plant (Pistia 
stratiotes). You will readily see that they differ considerably 
rom one another in external shape and in the mode of growth, 
although they were all taken in the Museum tank in Calcutta 
about the same time of the year. 
In concluding this lecture I wish to thank those who 
have assisted the Indian Museum in the work we have 
undertaken, especially in that of surveying the freshwater 
. fauna of India. A great deal of this work can only be pres 

reer erences anette sanies 
__! Cf. Miss Jane Stephens’ remarks on Irish species: Proc. Roy. 
Trish Acad. XXXI, pt. 60, p. 14 (1912). 

