324 GRIFFIN. 



fission is complete, and ordinary, normal growth is entered upon. In 

 contrast to this the micronucleus is active during only a very short period 

 of the division. Therefore, if a conclusion were to be drawn from the 

 behavior of the nuclei of Euplotes, it would be that the meganucleus is 

 not only the controlling organ in the metabolic activities of the ordinary 

 life of the animal, but it is also the active and directive agent of ordinary 

 (or vegetative) division, so far as any one portion of the cell can be 

 considered independently of the others; while the micronucleus is more 

 passive than directive, its part in division being limited to dividing in 

 such a way as to supply each daugliter cell with a micronucleus. This 

 division appears to be more of an incidental feature of fission than one of 

 the causative forces. 



DEVELOPMENT OF THE NEW PERISTOME. 



The nidiment of the new peristome appears simultaneously with or 

 shortly after the beginning of the reconstruction of the meganucleus 

 (Plate VI, figures 1 and 3), and in the form of a small, somewhat 

 elongated depression just back of the posterior margin of the old peri- 

 stome. The medial wall of the depression is nearly vertical, while the 

 lateral wall curves gently and evenly. The rudiments of a row of mem- 

 branelhe can be seen on the lateral wall in the earliest stages. These 

 first stages of peristome formation in £'. worcesteri are quite different 

 from the con-esponding ones of E. harpa as described by Wallengren. In 

 that form a triangular area of the eetosarc back of the old peristome 

 becomes clearer than the surrounding regions, and is definitely limited 

 between the posterior margin of the old peristome, the left-hand ventral 

 ridge, and a new temporary elevation. The invagination of the rudiment 

 of the new peristome occurs at the anterior end of this field, very close 

 to the border of the old peristome. Neither the clear ectosarcal field, 

 nor the external delimiting ridge' appear in Euplotes ivorcesteri, nor 

 does the rudiment of the new peristome lie so close to the border of the 

 old peristome in that species as in E. harpa. The extremely difficult 

 matter of finding early stages of the peristome formation in E. worcesteri 

 would have been rendered far easier if such a change in the eetosarc had 

 taken place. 



I have also found that the rudiments of the adoral membranellffi 

 appear considerably sooner in E. worcesteri than in E. harpa. The 

 further development of the new peristome to its full extent is nearly the 

 same in both species. The depression deepens and extends posteriorly, 

 not upon the surface but beneath the eetosarc, forming a short narrow 

 invagination. The mouth of the original depression becomes the open- 

 ing of the invagination, retaining for a time about the same size and 

 shape as first. The invagination now rapidly extends anteriorly until 

 it nearly reaches the micronucleus. I have seen the invagination pass- 



