INFUSORIA. l6l 



15. Trachelocerca (Fig. 123). 

 This will probably be a greater surprise to the ob- 

 server the first time he sees it than any other common 

 Infusorium, on account of the remarkable neck, which 

 can be stretched out to five or six times the length of 

 the body, and drawn back until it almost entirely disap- 

 pears The body, without the neck, is somewhat spipdle- 

 shaped, and occasionally ends in a short, tail-like re- 

 gion. The Infusorium is often concealed in a mass 

 of fragments or under a heap of dirt, with only that 

 wonderful neck visible, stretching and bending and 

 writhing like a colorless snake, as its searches the 

 slide for food. The end of the neck is rather pointed 

 and bears the mouth at the tip. The whole Infusuriom 

 is covered with fine cilia. It is common. 



16. Amphileptus (Fig. 124). 

 This is one of the largest of the free-swimming In- 

 fusoria, sometimes measuring yij- inch in length. The 

 neck is not extensile as in Trachelocerca, although it 





Fig. 124. — Amphileptus. 



is the longest part of the whole animal. The body, 

 exclusive of the neck, is somewhat spindle-shaped, taper- 

 ing more rapidly toward the rear than toward the front. 

 The latter or neck-like region is flexible and is capable of 

 being turned and twisted about in a way that often 

 suggests the movements of an elephant's trunk. The 

 whole body is covered with fine cilia. The mouth is at 

 the base of the neck, on the lower or ventral surface. 



