1 6 CALIFORNIA ACADEMY OF SCIENCES. [Proc. 3D Ser. 



of the animal (fig. 23). The ends curve upward along the 

 line of the left hand portion of each peristomal band (figs. 

 24 and 25), and each mass divides into two apparently 

 equal parts by transverse constriction (figs. 23 to 26). 

 The nuclear masses of each half gradually take the posi- 

 tion of the adult nuclear chain (figs. 27 to 30) and divide 

 into segments within a common membrane, which later 

 divides also. Gruber (18841:?) questions as to whether the 

 nuclei are connected by a membrane as in some other mul- 

 tinucleate forms. The majority of adult forms in this spe- 

 cies and all specimens approaching division have separate 

 nuclei, while a few fully grown individuals, probably recent 

 products of division, show some nuclei still connected by a 

 membrane. These conditions are plainly shown in iron- 

 haematoxylin and safranin stained sections and in material 

 stained with safranin in toto. 



No very definite structure has been made out in dividing 

 nuclei. In fresh material treated with formalin, acetic acid, 

 osmic vapor, picro-acetic, or picro-carmine, a distinct longi- 

 tudinal striation is visible in the nuclear masses of advanced 

 stages (figs. 23 to 28 and 82), and a skein-like appearance 

 in those of earlier stages (fig. 22) ; but other than this 

 they appear homogeneous. 



Peristomal Band and Axial Fibre. — The original peri- 

 stome, cilia, and mouth change but little during division. 

 The axial fibre appears unchanged both in sections and in 

 in toto preparations through stage 23, but in sections cor- 

 responding to stage 24, though still attached by a branch- 

 ing base to the cup, the fibre is thinner aborally, and in 

 later stages (figs. 24 to 27) it is not connected with the 

 dividing cup. 



New Peristome. — The first morphological indication of 

 division, with the exception of increase in size, is the 

 appearance on the right side of the oral disc, midway 

 between the union of the oral disc with the neck and the 

 posterior extremity of the body, of a small oval patch of 

 short cilia (fig. 18, ^•), which in the earliest stages, seen 



