PEOTOZOA AND SPONGES. 431 



ciliated surface of au Infusoiy, and the liuinan eye sees 

 more perfectly than 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 requirements of the lowest 

 organism are met adequately by its humble en- 

 dowments. 



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 neigh- 

 bourhood. 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 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 influence the result ; which yet one 

 may often give a shrewd guess at. Generally speak- 

 ing, small ponds, in which a good deal of sub-aquatic 

 vegetation grows — and jDarticularly if this be of a 

 minutely-divided character, such as MyriaphyUum^ 



