:{32 GRIFFIN. 



month and jjliaryiix remain open, the pharyngeal membranellag being or- 

 dinarily active; the edges of the peristome remain as sharp as ever, and 

 there are no signs of destruction of the adoral membranellae. I am 

 convinced that the old peristome continues unchanged in the anterior 

 daughter body. 



The suggestion made by Wallengren that the reason for the complicated 

 development of new cirri and absorption of old ones among Hypotricha 

 lies in the fact that the mother organs are not adapted to the needs of 

 the daughter cells either in size or position, seems to me not entirely 

 sufficient. It is often found that the new anal cirri of the posterior 

 daughter body before division are not to be distinguished from the 

 remaining old ones except by position. The same holds true occasionally 

 for the frontal ciiTi. Division takes place in such manner that the 

 explanation suggested by Wallengren must be true of part of the cirri. It 

 does not appear to account sufficiently for the replacement and absorption 

 of the cirri which are so placed that division does not seriously affect their 

 position or action. However, in Euplotes harpa the shape of the body 

 and the manner in which division occurs are such as to give color to 

 Wallengren's suggestion. 



DIVISIOX or THE BODY. 



Constriction of the body does not appear until the new cirri are all 

 present (except the light marginals) and have moved nearly 'to their 

 final positions (Plate VIII, figure 34) ; until the new peristome is 

 widely open and has been dra'nii backward a considerable distance by the 

 elongation of the body (note the difference in the distance from the 

 anterior to the posterior pharynx in figures 25 and 3-i, Plates YI and 

 YIII) ; imtil after the mieronucleus has divided and the two daughter 

 micronuclei have moved apart to their final positions, and the meganucleus 

 lias passed from the stage of concentration to that of elongation (Plate 

 VI, figure 25, and Plate VII, figure 26). The constriction deepens 

 rapidly, and separates the bodies in from one to two hours. An animal 

 which is preparing for division is almost always considerably broader and 

 more ovoid in outline than a "resting'' individual. (Compare figures 

 1, 3, 25, and others, with 28 and 29, where the bodies have attained an 

 almost typical shape before division is completed.) Even before con- 

 striction commences the body begins to grow longer and narrower. 

 (Plate VIII, figure 33.) This change is caused by the backward growth 

 of the region back of the old mouth, whieb. will become the posterior 

 individual. The movement is not simply an elongation or even an 

 increase in mass of the posterior part of the body, but is brought about by 

 the withdrawal of some material from the anterior portion of the body. 

 That'this must be so is proved by the backward movement of the invagina- 

 tion of the new peristome, which is pulled out from over the old peristome 

 (Plate VIII, figures 33, 3-i, 35, Plate VII. figure 26) and by the fact that 



