42 



Observations on the Fresh-water Sponges. 



By J. G. Waller. 



(Read April 26th, 1872.; 



On the Fresli -water Sponges more has been written, than on any 

 other genus of this order of the Protozoa. This may be accounted 

 for in the ease with which they are found, and in consequence their 

 examination involves but little difficulty. It is not, therefore, my 

 intention to aim at anything like completeness, but strictly to con- 

 fine myself to that which the title of my paper suggests, viz., 

 " Observations." This relieves me from the dangerous temptation 

 to theorise, and thus I believe I shall do my duty best to myself 

 and to you. I shall divide my task into two parts. In the first I 

 shall give a general glance at the organisms under consideration, 

 then a series of observations carried on with the growing sponge 

 during three months, in which time I made drawings and memor- 

 anda daily, illustrating every change which took place. 



The two Fresh-water Sponges, known in England, are dis- 

 tinguished as " Spongilla lacustris," and " Spongilla fluviatilis," 

 literally the Lake and the River Sponge. These terms were given 

 by Dr. Johnston, and are now generally accepted. Though they 

 are thus distinguished, they may often be found growing in the 

 same locality, under the same conditions, and within a few feet of 

 each other. 



The two are strikingly dissimilar, and yet their characteristics 

 have been often confounded. S. lacustris grows in long, lobular, 

 branching forms ; S. jluviatilis in large masses, without symmetry. 

 Yet it has been asserted, that the latter is also found with 

 lobular projections, and Dr. Bowerbank suggests that this may be 

 due to it having originally been parasitic on some Alga. I have 

 myself seen several examples of this form, but arrive at quite another 

 conclusion. At least, in those instances which have come under 

 my observation, this was certainly not the cause, but a confervoid 



