PROTOZOA AND SPONGES. 877 



the loose aggregation of pigment granules on the edge of 

 a Medusa. But this diversity is essential to creation, as 

 the great and wondrous plan which we see it to be ; and, 

 meanwhile, we may rest satisfied that the humble require- 

 ments 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 which have been 

 dipped into the fresh-water ponds in the neighbourhood. 

 All collections 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 

 animalcules. 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 

 animalcule. 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 expe- 

 rience 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, influence the result, which 

 yet one may often give a shrewd guess at. Gener- 

 ally speaking, small ponds, in which there is a good 

 deal of vegetation below the surface and particularly if 

 this be of a minutely-divided character, such as Myrio- 

 phyUum, Chara, &c. and whose surface is well covered 

 with duckweed (Lemna), yield well ; and, in collecting, it 

 is desirable so to dip as that some of the fine loose sedi- 

 ment of the bottom may flow into your phial, and then to 

 pluck up one or more of the filamentous water-plants, and 

 introduce these into your vessel. 



