EUPLOTES WORCESTER!: I. 309 



the nucleus shortens and becomes thicker. The thickening ma}- take 

 place only around the vacuoles, while the intervening portions become 

 dra'^^Ti out into fine connecting threads, which finally break. Division 

 may begin during this vacuolated condition of the meganucleus, but 

 apparently does not proceed to a normal conclusion. 



The micronucleus (Plate III, figure 9) is single, lying in or near a 

 shallow depression on the left side of the meganucleus. I believe that 

 the forms possessing two niicronuclei, which are very common at times, 

 belong to a stage following conjugation. 



The micronucleus contains a sparse reticulum of chromatin. (Plate 

 IV, figures 1, 2, 3.) Ordinarily the entire micronucleus stains uni- 

 formly, but with careful extraction of the stain the reticulum is rendered 

 visible. 'If extraction is not quite sufficient, the micronucleus appears 

 homogeneous, as if composed of a uniformly staining colloid substance. 



Systematic position. — In order to distinguish Euplotes worcesteri from 

 Euplotes vanntis 0. F. M., one must depend largely upon the careful 

 work of Minkiewicz for exact Imowledge of the structure of the European 

 form. In the shape of the body, and in the number, form, and arrange- 

 ment of the cirri, the Philippine form is exactly like the European. 



Euplotes worcesteri has a longer pharynx than E. vannus 0. P. M. 

 and twentj' to thirty membranellse inside the pharj'nx instead of eight. 

 Both the length of the phan'nx and the number of p)haryngeal membra- 

 nellse vary, but I have always found the number of these membranellee to 

 be more than double that given for E. vannus by Minkiewicz. 



Minkiewicz presents one figure showing ten rows of sensor}- bristles 

 on the dorsal surface of E. vannus. I find that most specimens of E. 

 worcesteri have eight rows, altho'Ugh six, seven, nine, 

 or ten rows are sometimes found. As there may be 

 considerable variation in the number of these rows 

 in E. vannus also, 'we are not justified in considering 

 the apparent difference between the species in this 

 regard as a valid specific distinction. 



The most important diflierence, and the one upon 

 which the diagnosis of the species really depends is U } 



in the shape of the posterior end of the meganucleus. f Q 



As may be seen by referring to text figure 13 this j-jg is.— Drawings ot 

 end of the nucleus is enlarged in a very character- the meganuciei ot 



- , • -KIT' 1 • ■ ■ . ,. ' ™ ,T Euplotes vannus O. 



istic manner. Mmkiewiez gives six figures of the p. m., copied from 

 meganucleus, all of which represent its end as being Minkiewicz (Plate ii, 

 turned back upon itself, without any enlargement. ""'^'^ " *' 

 (Text figure 13.) The general appearance produced is much the same 

 as is seen in E. worcesteri, but the structure is entirely different. 



Wliether differences exist in the arrangement of the ventral sensory 



997 



