42 



LOWER INVERTEBRATES. 



animal somewhat contracted. It is capable of great distention, so as to become fifteen 

 or twenty times longer than broad ; it then attains a length of one-twelfth of an inch, 

 or even more. Its cylindrical body, sometimes flattened, is rounded at the extremities, 

 often truncate posteriorly. The single line of peristomal hairs extends down the 

 left side of the anterior ventral face to the oral aperture, situated near the middle of 

 the body. The remarkable contractile vesicle and nucleus have been referred to al- 

 ready. The generic name was given on account of the apparently spiral peristome, as 

 seen when the animal twists itself about its long axis. The writer recently found this 



species so abundant on a scarcely submerged moss 

 that the water taken up by a dipping-bottle was 

 rendei-ed turbid by them. The solution of tannin 

 in glycerine, previously referred to, appears to be 

 a valuable reagent for studying this animalcule. 



The Stentors, or trumpet animalcules, are 

 among the most entertaining heterotrichous In- 

 fusoria. They are large, active, and often highly 

 colored, so that a colony of them incessantly ex- 

 tending and retracting their bodies, at the same 

 time driving, by means of their oral ciUa, strong 

 currents of water against their peristomial sur- 

 faces, presents a scene, when well defined by the 

 microscope, not soon to be forgotten. The ex- 

 cellent cut (Fig. 42) of Stentor polymorphus, a 

 widely-distributed form, displays the characteris- 

 tics of the genus far better than words can do. 

 The Stentors often secrete gelatinous sheaths, 

 which sometimes embrace several individuals. 



This group has, too, its species which secrete 

 a lorica, and as in other cases they are very attrac- 

 tive objects. An exainple may be cited in Fol- 

 liculina: its flask-shaped sheath is attached by 

 the side, the neck being bent upwards. The 

 animal closely resembles a Stentor, except that 

 the peristome is two-lobed, instead of nearly cir- 

 cular. The species are defined according to the 

 shape of these lobes. Folliculina ampulla has 

 been found in America by Dr. Leidy. In Chmtospira the two lobes give place to 

 a slender ribbon-like extension of the anterior region, which, when extended, is twisted 

 into a spire ; a hyaline expansion also extends laterally along the broad part of the 

 peristome, giving the extended zooid a unique appearance. It is not attached to its 

 surrounding sheath. The preceding loricate forms are sedentary ; on the other hand, 

 Tintinnus includes free-swimming species. The beautiful tests of these are common 

 in the water-supplies of most American cities. 



In the genus Codonella there are an outer circle of twenty tentacle-like cilia, and an 

 inner one of lapj)et-like appendages ; the case is similar to that of the preceding. 



Fig. 42. — Stentor polymorphus. n. Nucleus. 

 CD. Contractile vacuole. Magnified 90 times. 



