1H THE OCEAN WORLD. 



live in stagnant waters, feeding on the debris of aquatic plants, from 

 which they draw their chief nourishment as well as their colour. 



The Bursarians are animals with an oval or oblong contractile 

 body, provided also with vibratile cilia, especially on the surface, having 

 also a large mouth, surrounded with cilia, forming a sort of microscopic 

 moustache, spirally arranged. 



Among the species belonging to this group may be noted the Con- 

 dylostoma patens (Fig. 39), remarkable for its size and voracity. It 

 sometimes attains the twelfth of an inch, and abounds on every shore 

 from the Mediterranean to the Baltic. Another Bursarian, a species 

 of Pfagiostoma, lives between the intestines and the external muscular 

 bed of the earth-worm, Lumbricus terrestris. To the group of 

 Urceolarians belong the Stentors, which are in number the most 

 numerous of the Infusoria; they are, for the most part, visible to 

 the naked eye. 



The Stentor s are inhabitants of fresh, tranquil water, not subject 

 to agitation, and covered with water plants. They are nearly all 

 coloured green, blackish, or blue ; their bodies 

 covered with cilia. They are eminently con- 

 tractile, and very variable in form. They can 

 attach themselves temporarily, by means of the 

 cils at their posterior extremities, when they 

 assume a trumpet-like form, the bell of which 

 is closed by a convex membrane, the edge 

 being furnished with a row of very strong 

 obliquely-placed cilia, ranged in a spiral, meet- 

 ing at the mouth, which is placed near this 

 edge. When they swim freely, they alter- 

 nately resemble a club, a spindle, or a sphere. 

 The Stentor Muelleri is seen in ponds in the 

 neighbourhood of Paris and elsewhere ; it has 

 been found even in the basins of the Jardins 

 des Plantes (Fig. 40). 



The animals which constitute this genus are 

 fixed in the first part of their existence, but 

 free in the second. So long as they are fixed, 

 they resemble, in their expanding state, a bell 

 or funnel, with the edges reversed and ciliate. When they become 



i*. 40. Stentor Muelleri (Enr.), 

 magnified 75 times. 



