THE ANIMAL WORLD OF WELL-WATERS. 



255 



...v* 



W(f..... 



Dtj 



Fig. 5. 



pseudopodium, which has grown to be permanent, and which 

 has a certain function to exercise, namely, to make motions of 

 rowing and feeling. 



Starting with the 

 amoeba, the flagellate 

 infusoria represent the 

 next higher phase of 

 morphological differ- 

 entiation — that is to 

 say, they represent the 

 division of the homo- 

 geneous substance of 

 the amoeba into distinct 

 parts, to which different 

 functions are assigned. 

 In social science one 

 would allude to this as 

 the commencement of a 

 division of labor. 



Fig. 5 represents an individual belonging to the genus Cothur- 

 nia, which is very frequently found in the depths of town and 

 country wells. It possesses the power to withdraw with light- 

 ning speed into the trans- 

 parent envelope which sur- 

 rounds it whenever the cilia 

 which are attached to its 

 front come in contact with 

 anything hard. K denotes 

 the nucleus which no infu- 

 soria lack, and v represents 

 the vacuole, which, however, 

 at times may disappear. 



Fig. 6 pictures a small 

 creature, the Stenostonia leu- 

 cops, which attains a length 

 of about one millimetre, and 

 which appears to the naked 

 eye like a minute white 

 thread. This kind of worm 

 is of frequent occurrence, and 

 has received its name from 

 the rotary motion which the 

 cilia that are on the surface of 

 its body impart to the water when the animal moves or swims : g g, 

 is the nerve-center (brain-ganglion), which is very considerable in 

 proportion to the size of the worm. The mouth is not shown in 



Fig. 7. 



