EUPLOTES WORCESTERI: II. 333 



the anterior half of the body becomes naiTOwer at the same time. As the 

 new peristome moves backward its anterior end is bent to the right; the 

 fact that tlie inclination toward the right is greater at first than the amount 

 of constriction of the body, indicates that pressure exerted by the latter 

 process is not the sole cause of the bending, but that internal directive 

 forces (or tensions) of considerable strength exist. This is still more 

 clearly shown by Euplotes harpa, in which the i^eristome is bent to a right 

 angle before constriction begins. The further bending and extension of 

 the peristome across the anterior end of the new body proceeds at the same 

 rate as the constriction, and appears to be produced by it. It is impos- 

 sible to sa}' certainly whether new adoral membranellfe are formed as 

 the zone extends across the front of the body or not, but it seems more 

 probable that all the membranellas are formed in the invaginated per- 

 istomial cavity before this movement commences, and that increase in 

 the length of the zone is secured by intercalary growth only. The basis 

 for this supposition is that the number of membranellee in the invagination 

 (Plate VII, figure 32, Plate VIII, figure 33) is equal to the entire 

 number generally found in the adoral zone and pharynx of an adult 

 Euplotes. 



The extension of the adoral zone toward the right forces the connection 

 between the bodies to remain at that side. (Plate VII, figures 28, 29.) 

 As the constriction is carried across the body, the thin ventral wall of the 

 remaining part of the peristomial cavity (Plate A'^III, figure 36) is 

 broken through ; a portion remaining may form the marginal lamella of 

 the medial wall of the completed peristome. (Plate A''II. figures 28 

 and 29.) 



The stalk connecting the daughter bodies is sometimes drawn out into 

 a slender thread of some length; it is not unusual to see a pair of 

 individuals swimming rapidly about connected in this manner, the 

 posterior one swinging from side to side as if the two were engaged in 

 a game of crack-the-whip. By the time that separation occurs the two 

 bodies may have their usual form, or they may be of such shapes that 

 the observer can very easily be certain which was anterior and which 

 posterior before division. (Plate VII, figures 30 and 31.) A new 

 contractile vacuole appears in the anterior body before fission is complete. 



LITEEATURE. 



Balbiani, 6. Eecherches sur les pheuomfenes sexuals des Infusoires. Journ. de 



la Physiol. T. N. Paris (1861), 102-130, 174-220, 431-438, 465-520; pi. 7-9. 

 Idem. Sur la structure et la division du noyau chez le Spiroohona gemmipara. 



Ann. de Microgr. (1895), 7, 289. 

 BiiTSCHLl, 0. Studien ii. d. ersten Entwickhitigsvorgitnge d. Eizelle, d. Zell- 



theilung, und die Conjugation der Infusorien. Prankf. Abhandl. d. Senckenh. 



Oesells. Naturf. Freunde (1876), 10, 213-452; 15 pi. 

 Idem. Protozoa. Bronn's Klassen und Ordnungen des Thier-Reichs. (1887-89), 



1, Abt. III. Infusoria. 



