1887.] NATURAL SCIENCES OP rHILADELPHIA. 16o 



they have been found in great abundance and of a very histy growth. 

 Of all discouraging situations it is almost hopeless to look for them 

 in shallow water having a mud bottom. Mud is their great enemy,, 

 as gravity aids their natural currents to fill the cavities with earthy 

 matters that soon suffocate them, because the latter are too feeble to> 

 throw them off. Of course in any body of water liable to be 

 charged with sedimentary material, the principle of natural selection 

 favors those growing on the lower side of their bases of support, 

 which protect them from the intrusion of the heavier particles. 



For that reason perpendicular and water logged or floating timbers, 

 submerged stumps of trees, and branches drooping into the water 

 from trees or bushes along the banks, are favorite locations. They 

 do not disdain more temporary support, such as weeds and water- 

 grasses. I have received from a friend, specimens growing upon 

 water plants that wild ducks had torn from the bottom, and that 

 were found floating upon the surface of Lake Michigan. Through 

 the clear water of our northei-n lakes, we may often see them lying 

 in slender lines upon the leaves of submerged weeds, or in beautiful 

 cushion-like masses upon the stones or gravel. 



In my explorations I have had much satisfaction in the use of a 

 long pole, to which was attached a small net, with one part of its 

 edge shaped into a scraper, like a garden hoe. This enabled me to 

 examine the surface of timbers at a depth of eight or ten feet and to tear 

 off and bring up sponges from that depth ; beyond which all is to me an 

 "aqua incognita." Biologists labor at some disadvantage in studying 

 the fiiuna of our fresh water, as compared with the facilities offered 

 them in collecting ocean subjects. The nets and dredges of many 

 exploring expeditions have, at least, begun to acquaint us with the 

 inhabitants of the "deep sea;" but who knows anything about the 

 fauna or the flora of our deep fresh-water lakes, or even of our 

 larger streams? The largest specimens of this group ever reported, 

 were dredged from the bottom of Lake Baikal in Central Asia, 

 (Lubomirskla). I know of no similar attempts to collect them else- 

 where. It is to be hoped that means may be found ere long to 

 make such explorations, which must result in an increase of 

 knowledge in many lines. Meantime no opportunity offered by the 

 accidental or designed drainage of artificial reservoirs should be 

 neglected. I have spent hours of great pleasure and profit while 

 groping around the distributing reservoirs upon Fairmount Hill, 

 Philadelphia, at times when the water was drawn ott' for cleaning 

 or repairs. 



