EUPLOTES WORCESTERI: II. 331 



as has been mentioned, it was finally observed that after the peristomial 

 aperture has grown to a large size a ridge arises, beginning at the 

 anterior angle of the mouth, and passing forward lateral to the cirrus just 

 described. (Plate VIII, figiires 34 and 35.) This ridge becomes the 

 medial wall of the completed peristome, while the original medial margin 

 of the peristomial aperture and part of the medial wall of the cavity 

 become included in the ventral surface of the body. (Plates VII and 

 VIII, figures 26, 34, 35, 36.) In this manner the cirrus arising in the 

 peristomial cavity also becomes shifted to the ventral surface, and lies 

 not far from its final position of frontal cirrus 4. (See / and / 4.) 



The development of the left marginal cirri presents no noteworthy 

 features. These cirri have reached their final positions and proportions 

 by the time the bodies separate. Eight marginals are formed upon the 

 margins of both daughter bodies before final separation takes place, but 

 were not observed in any of the specimens drawn. 



The final disposition of the cirri is exactly the same in Euplotes 

 iroircsteri as in E. harpa. While the figiires of Minkiewicz of E. vannus 

 are very incomplete, the process is evidently the same in that species. 



Sensory bristles. — At an early stage in the development of the cirri; 

 numerous additional groups of granules appear upon the ventral surface. 

 Their positions bear an evident relation to the new cirri. As each group 

 of granules of the adult Euplotes surrounds the base of a sensory bristle, 

 the same relation must be true of the new granules, although the direct 

 observation of the bristles at this stage is practically impossible. I have 

 not been able to decide whether the old sensory bristles all disappear and 

 are replaced by new ones, or whether new bristles appear only in those 

 portions of the two new bodies which otherwise would be left without 

 any by the divisioii. 



The sensory bristles of the dorsal surface and their related groups of 

 granules do not show any changes before division. Kew bristles appar- 

 ently are interpolated in the dorsal rows during the period of growth 

 which succeeds fission. 



It has been known for many years that the old peristome, which is 

 retained by the anterior daughter body, is not always retained without 

 change. Confining ourselves to the genus Euplotes the only author who 

 has mentioned in detail these changes in the old peristome is Wallengren. 

 He finds that the mouth of Euplotes harpa atrophies so that neither food 

 nor water is taken in during the later stages of fission. iSTeither his 

 figures nor his description throw any more light upon this point. He 

 also observed that just before division takes place the lower lip becomes 

 filled with a great number of round granules. He did not observe any 

 other changes in the form or structure of the peristome, nor any recon- 

 struction of the adoral zone. I have been unable to observe any changes 

 whatever in the old peristome of E. worcesteri during division. The 



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