496 JOHNSON. [Vol. VIII. 



Gruber ('84®), Jickeli ('84), and others have described as occur- 

 ring in various Infusoria. In preparations of Paramecium 

 candatiim, showing that form at many stages of fission, I have 

 been equally unsuccessful in finding a longitudinal arrange- 

 ment of chromatic threads. Furthermore, in R. Hertwig's 

 ('89) beautiful memoir on the conjugation of Parafnecmm aiire- 

 lia, a figure of that species in fission is given, but the strongly 

 constricted meganucleus has no trace of striation. I believe, 

 therefore, that any attempt to regard the longitudinal arrange- 

 ment of chromatic threads a constant feature of meganuclear 

 division, and adduce it as evidence of a disguised mitosis, is 

 unwarranted. 1 



In moniliform nuclei both chromatic granules and network 

 are restricted to the nodes, and do not extend into the 

 commissures unless the latter are unusually thick (Figs. 19, 

 44, 45). In any case, the commissures doubtless contain a 

 thread of the non-stainable, semi-fluid portion of the nucleus, 

 the karyoplasm. The karyoplasm is so charged with granular 

 chromatin that it is seldom distinguishable as a separate 

 substance. The translucent oval bodies, looking like vacuoles, 

 which are frequently present in the meganuclei of all Stentors 

 (Figs. 19, 20), are probably to be regarded as segregations of 

 karyoplasm free from chromatin. Each globule occasionally 

 contains a minute, slightly-stainable, denser, and refractive 

 body, the nature of which I am ignorant (Fig. 20).^ It is not a 

 micronucleus, for it frequently lies deep within the meganucleus. 



An interesting fact in regard to the meganuclei of 5". ignetis 

 and S. pyrifovDiis is that they undergo division independently 

 of that of the cytosome (Figs. 22-24). Indeed, the vast 

 majority of individuals of both the above-named species have 

 two or more entirely separate meganuclei. I have, besides, 

 found nuclei in every stage of constriction. Owing to the 

 frequent occurrence among the Ciliata of moniliform nuclei 

 with very attenuate commissures, it has been held by some 



1 In a previous article ('92, p. 155) I have taken the ground that the appear- 

 ance of longitudinal threads in a dividing nucleus is not m itself evidence of 

 mitosis. 



2 This is evidently the structure figured by Stein in the nodes of 5". polymorphus 

 ('67, Taf. V, Figs. 7, 9, 12). 



