THE CILIATE INFUSORIA. 



37 



opens, allows the rejected matter to pass out, and then 

 closes over, leaving no trace of an outlet. This and other 

 Infusoria seem, then, to have a definite digestive tract, hol- 

 lowed out of the parenchyma of the body. 



" The system," says Clark, " which is analogous to the 

 blood-circulation of the higher animals, is represented in 

 Paramecium by two contractile vesicles (cv, cv l , I, n, in), 

 Itoth of which have a degree of complication which, per- 

 haps, exceeds that of any other similar organ" in these ani- 

 mals. When fully expanded they appear round, as at c v ; 

 but when contracted they appear, observes Clark, as " fine 

 -radiating streaks, and as the main portion lessens they grad- 

 ually broaden and swell until the former is emptied and 

 nearly invisible, and 

 they are extended 

 -over half the length 

 -of the body. In this 

 condition they might 

 be compared to the 

 .arterial vessels of the 

 more elevated classes 

 of animals, but they 

 would at the same 

 time represent the 

 veins, since they 

 .serve at the next moment to return the fluid to the main 

 reservoir again, which is effected in this very remarkable 

 way." The contents of these vesicles is a clear fluid. 



The reproductive organ in Paramecium is a small tube 

 (), only seen at the reproductive period when the eggs (ti) 

 are fully grown. Clark says that the eggs are arranged in 

 it " in a single line, one after the other, at varying dis- 

 tances." It usually lies in the midst of the body, and ex- 

 tends from one half to two thirds of the length of the ani- 

 mal. The eggs pass out from the so-called ovary through 

 an aperture near the mouth. Lasso-cells like those in the 

 jelly-fishes are said by Biitschli to exist in an infusorian 

 named by him Polykrikos. 



In the trumpet animalcule (Fig. 25, Stentor polymor- 



Fig. 6 Process of fission in Slentor polymorphns. 

 b, a new Steutor budding out; e, ready to separate from 

 the original one;./', the two in a contracted state. 

 After Cox. 



