EUPLOTES WORCESTER!: I. 



307 



about one minute, thirteen showed no vacuole, while in some of the 

 remaining seven which had vacuoles, these were very small. In a less 

 careful examination the con- 

 tractile vacuole was visible in onlj' 

 four out of &itj, but I afterwards 

 found that the vacuole is so 

 minute for some minutes as to be 

 nearly invisible even with high 

 powers. 



The contractile vacuole in 

 Euplotidse is said to open upon 

 the ventral surface of the body 

 beside or in front of the anus, 

 but I have not been able to make 

 any observations regarding this 

 point, except to be certain that 

 it does not open in front of the 

 anus in E. worcesteri. 



Nuclei. — The shape of the 

 meganucleus is shown by text 

 figure 10. The enlargement of 

 the posterior end, reminding one 

 of an anchor-fluke, is a most char- 

 actei'istic feature of this species 

 of Euplotes. While it is subject 

 to variation, so that the enlarge- 

 ment is not of exactly the same 

 size nor shape in any two speci- 

 mens, the general form is almost 

 always the same, and so marked 

 as to constititute one of the 

 diagnostic characters of the 

 species. Minkiewicz represents 

 (text figTire 13) the corresponding 

 end of the meganucleus of E. 

 vannus 0. F. M. as turned back 

 upon itself, but not enlarged. It 

 does not seem possible that there could be a mistake in so simple an 

 observation. The difference in the shape of this part of the meganucleus 

 forms a very convenient means of distinguishing the two species, which 

 otherwise are much alike. 



The portion of the nucleus which crosses' the anterior end of the 

 body is also considerably thickened and the anterior margin is frequently 

 irregular. 



99456 2 



Pig. 10. — ^Various shapes assumed by the 

 meganucleus of Euplotes worcesteri n. sp. 



