VORTICELLA 209 



endoplasm near the middle of the body. The endoplasm has 

 much the same character as that of Paramecium, con- 

 taining food-vacuoles, pellets, and granules, which move round 

 and round in a regular cyclosis. 



Close alongside of the gullet is a large clear space, which is 

 stationary and generally distinguished -from the food-vacuoles 

 by its larger size. This cavity is filled with fluid, and com- 

 municates by a very narrow passage with the vestibule ; it is a 

 reservoir like that already described in Euglena. Close beside 

 it is a contractile vacuole, whose contents at every contraction 

 are poured into the reservoir, whence they are slowly emptied 

 into the vestibule, and so to the exterior. 



Like Paramecium, Vorticella is in need of a special aperture 

 for the expulsion of undigested matter and solid excreta. This 

 aperture is situated in the vestibule close to the opening of the 

 reservoir, and is generally known as the anus. It is often a 

 permanent opening with a short and narrow tube leading to 

 the endoplasm, but these relations vary very much in different 

 species. 



A macronucleus and a micronucleus are present. The former 

 is very large and elongated. In some species it has the form 

 of a horse-shoe, in others it is like a twisted riband. Its shape 

 and position in V. monilata can be better understood from an 

 inspection of fig. 44, A, than from any description. The micro- 

 nucleus is small, and is placed close alongside of the macro- 

 nucleus in the anterior end of the body. The micronucleus 

 stains with great difficulty, whereas the macronucleus seizes on 

 the ordinary dyes with great avidity and obscures all the 

 structures lying against it. Hence the micronucleus is difficult 

 to see, but it can usually be demonstrated in living specimens, 

 and better still in specimens cleared in glycerine after being 

 killed in a 10 % solution of corrosive sublimate to which a few 

 drops of acetic acid have been added. 



Vorticella reproduces itself by binary longitudinal fission. 

 The peristome is contracted, and the body becomes depressed 

 and transversely elongated. The macronucleus is straightened 

 and comes to lie transversely across the middle of the body, 

 forming a fibrillated spindle like that of a Paramecium preparing 

 for division. The micronucleus elongates to form a spindle 

 placed alongside of the macronuclear spindle and both become 

 dumb-bell shaped and divide. (Fig. 44, Z>.) A constriction 



