PROTOZOA AND SPONGES 423 



tiles on the edge of a Medusa. But this diversity is essen- 

 tial to creation, as the great and wondrous plan which we 

 see it to be; and, meanwhile, we may rest satisfied that 

 the humble requirements of the lowest organism are met 

 adequately by its humble endowments. 



This evening I propose to show you some of these 

 humble conditions of animal life the lowest of the lowly. 

 I have here two or three phials of very rich water dipped 

 from the fresh-water ponds in the neighborhood. All col- 

 lections of water are not equally productive; and very far 

 indeed is the popular notion from correctness that every 

 drop of water which we drink contains millions of ani- 

 malcules. You may find many collections of clear water, 

 springs, streams, and pools, from which you may examine 

 drop after drop in succession, with the highest powers of 

 the microscope, and scarcely discover a solitary animal- 

 cule. Again, it is not stagnant and fetid pools that are 

 the richest in vitality; though no doubt you will always 

 obtain some forms abundantly enough in such conditions. 

 According to my own experience an experience of many 

 years the paucity or profusion of animal life in any given 

 collection of water can never be determined beforehand; 

 the season, the situation, the aspect, the character of the 

 country, and many other unsuspected conditions, may in- 

 fluence the result; which yet one may often give a shrewd 

 guess at. Generally speaking, small ponds, in which a 

 good deal of sub- aquatic vegetation grows and particu- 

 larly if this be of a minutely -divided character, such as 

 Myriopliyllum, Chara, etc. and whose surface is well cov- 

 ered with duckweed (Lemna), yield well; and, in collect- 

 ing, it is desirable so to dip as that some of the fine loose 

 sediment of the bottom may flow into your phial, and then 



