284 



FRESH-WATER BIOLOGY 



110 (109) Body spiral, cylindrical, somewhat pointed at both ends, but con- 

 tractile; peristome spiral with the mouth near the middle 

 of the body. Membranellae on the left side of the peri- 

 stome, a membrane on the right side. 



Metopus Claparede and Lachmann. 

 Representative species Metopus sigmoides Miiller 1786. 



Cilia usually longer at the posterior end. A mass of dark pigment gran- 

 ules in the anterior extremity. Nucleus oval, central; contractile vacuole 

 posterior. Length lOo to 200 u. At the bottom of infusions. Metopides 

 acuminata Stokes diiiers from the above species in the posterior, tail-like 

 prolongation from which extend a number of long bristles. It is also 

 smaller in size. 



i^jCTIacn 



Fig. 508. Metopus sigmoides. 



, contractile vacuole; macn, macronucleus. X 220. 

 (After Stein.) 



(108) Without an undulating membrane. Body greatly elongated, cyl- 

 indrical, contractile. Peristome reaching to the middle of 

 the body. Strong membranellae on the left side of the peri- 

 stome. Body spirally striated. Spirostomum Ehrenberg. 

 Representative species. Spirostomum ambiguum Ehrenberg 1835. 



3 Body ten to fifteen times as long as 



broad, but readily contracting into a short 

 spiral body. Nucleus moniliform. Con- 

 tractile vacuole posterior, extending for- 

 ward as a canal. Extended body may 



T^„ r,.- , ,. .. ..., T reach 2800 u in length. Common among 



Fig. 509. Sptrostomum ambiguum. ct, contractile vacuole; +■ 1 + 



macn. macronucleus. X 30. (After Kent.) aquatic plants. 



112 (107) Peristome a broad triangular area, deeply sunken. 



"3 



113 (114) With an undulating membrane on the right side of the peristome. 

 Body cylindrical or purse-shaped, sometimes contractile. 

 Peristome broad in front extending one-third the length of 



the body Condylostoma Dujardin. 



Representative species. . . Condylostoma patens Miiller 1786. 



Body broadly ovate, widest posteriorly. Peristome broadly triangular, 

 extending about half the length of the body. Nucleus moniliform; con- 

 tractile vacuole irregular. Length 200 n. Stagnant water. 



Fig. 510. 



Condylostoma patens, macn, macronucleus; 

 X 105. (After Kent.) 



u, undulating membrane 



