316 GRIFFIN. 



gren's paper I liave added nothing to my own except the necessary 

 critical comparisons; the observations stand as originally made. 



It is evident that processes of divison must be much alike in all the 

 species of the genus Euplotes, though such differences exist as to render a 

 comparative study extremely interesting. In considering the process of 

 division I have omitted all reference to the divisions of conjugation and 

 to the construction and resoqjtion of organs during that phase, because 

 my study of conjugation in Euplotes worcesieri, so far very incomplete,, 

 has convinced me that these processes are quite different from the ones 

 of ordinary division. It has proved easy to keep the strain alive in the 

 laboratory for more than a year and a half, and to secure an abundance 

 of material for study and preparation in every possible manner. The 

 result has been not only to prove that the new peristome is actually 

 foiTned by an invagination, but also to reveal other curious processes 

 connected with division. After an intimate study of a protozoan like 

 this, one can appreciate the full force and meaning of the statement that 

 many of the protozoa are not simple, but extremely complex animals. 



The process of division of Euplotes worcesteri includes two stages, 

 one of preparation, the other that of actual division of the body and mega- 

 nucleus. During each stage a definite series of changes occurs in nearly 

 every organ of the body. The stage of preparation for division includes 

 the reconstruction and concentration of the meganucleus, the invagination 

 of the rudiment of the new peristome, the division of the micronucleus, 

 and the appearance of the new cirri. That of division includes the 

 constriction of the body and separation of its halves, the drawing of 

 the new peristome to the surface of the body and into its final shape and 

 position, completion of the new pharynx, division of the meganucleus, 

 absorption of the old cirri, and the shifting of the new cirri from the 

 places of their origins to their ultimate positions. 



EECONSTEUCTION OF THE MEGANUCLEUS. 



By this is meant that a progressive change occurs in which all the 

 chromatin of the meganucleus is actually dissolved and then recon- 

 structed. The first stage of this process is the appearance at each end of 

 the cord-shaped meganucleus of a band in which there is a complete 

 absence of the ordinary chromatin reticulum. It will be convenient to 

 refer to these as the reconstruction bands. They pass rapidly from the 

 ends of the nucleus toward the center, finally meeting, and then disap- 

 pearing. (Plates IV, V, and VI, figures 1, 3, 3, 4, 8, 10, 13, 14, 18, 20.) 

 Each band consists of two planes of about equal thickness, the one on 

 the central side staining darkly and uniformly, while the other is not 

 stained and consequently shows distinctly. Ko traces of a reticulum 

 or of chromatin granules can be seen in the first plane ; but the uniform 

 stain which this region takes indicates that the chromatin has here been 

 dissolved in the karyolymph; therefore, I call this the solution plane. 



