PROTOZOA AND SPONGES. 377 



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 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 from the fresh-water ponds in the neighbour- 

 hood. All collections of water are not equally pro- 

 ductive; 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. Accord- 

 ing 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 ud suspected conditions, in- 

 fluence the result, at which yet one may often give a 

 shrewd guess. Generally speaking, small ponds, in which 

 there is a good deal of vegetation below the surface, 

 and particularly if this be of a minutely divided cha- 

 racter, such as Myriophyllum, Char a, &c, and whose 

 surface is well covered with duckweed (Lemna), yield 

 well ; and, in collecting, it is desirable so to dip that 

 some of the fine loose sediment 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 it. 



