yo THE BIOLOGY OF STENTOR 



the "embryology" occurs before instead of after reproduction 

 (Johnson, 1893). (An exception is found in budding, such as chain 

 formation in lower worms in which new individualities are com- 

 pletely formed before separation, an analogy with protozoan 

 reproduction first suggested by Gruber (1885a).) A self-cutting or 

 fission line is indeed formed in StentoTy but it is neither the cause 

 nor the necessary result of the conversion of one individuality 

 into two. 



MultipHcation by fission in Stentor was first observed by 

 Trembley (1744). With continued refinement of the microscope, 

 further details of division were given by Stein (1867), Moxon 

 (1869), and Cox (1876); yet it remained for Schuberg (1890) to 

 provide the first really comprehensive account of what takes place. 

 Stentor division as a developmental process was beautifully and 

 accurately drawn in the illustrations of Johnson (1893) and 

 Schwartz (1935). Visible changes during division have been 

 designated as a numbered series of stages (Tartar, 1958c) and are 

 shown in Fig. 14. 



Restricting the story to the best-known species, coeruleus, the 

 first sign of the formation of a new individuality is a splitting of 

 the pigment stripes on a diagonal in the mid-ventral region 

 (Fig. 14-0), first noted by Stevens (1903) and very probably 

 representing the insertion of new clear bands. In this area of 

 stripe multiplication a rift soon appears as the very beginnings of 

 the new set of feeding organelles for the future posterior daughter 

 cell. This primordium lengthens at both ends according to 

 Johnson and broadens quickly to its definitive width while the 

 long oral cilia develop within it. At this time the anlage is usually 

 in the form of a crescent and this appearance is generally diagnostic 

 of an early divider. (Occasionally the anterior end of the primor- 

 dium may extend straight forward towards the old oral region, as 

 it does in reorganizing animals, so one cannot always be sure.) 

 There is increasing multiplication of stripes as pigment bands at 

 the anterior border of the primordium split into 2, 4, and 8 rows 

 (Fig. 15A) (Schwartz, 1935). It is these new, fine stripes embraced 

 by the presumptive membranellar band which will form the new 

 frontal field of the opisthe. Such additions may increase the 

 circumference of the cell according to Stevens and Schwartz, 

 though this is certainly not obvious. 



