430 metcalf: opalina and the ciliate infusoria 



telophase of mitosis. All species thus far mentioned in this 

 paragraph are Protoopalinae with characteristic protoopalinid 

 nuclei. Simplest in the genus Opalina is 0. lanceolata (of Bez- 

 zenberger) with four nuclei; then 0. mimuta (new species from 

 Bufo melanostictus) with from five to twelve nuclei; then very 

 many species with from one hundred to several thousand nuclei. 



It seems evident that the pleurinucleate condition in the 

 Opalinidae is due to some disturbance of the mitotic phenomena 

 and the usual nucleus-cytoplasm relation, nuclear mitosis and 

 body division being inhibited to a less or greater degree in dif- 

 ferent species. As this strange tendency develops we get finally 

 bodies with a great number of nuclei. Among the Opalinids 

 the culmination of this disturbance of the division phenomena is 

 seen in the new species, Opalina segmentata, in which species even 

 the vegetative fissions, which occur from time to time in both 

 multinucleate and binucleate species, are inhibited after they 

 have begun. Opalina segmentata is an elongated cylindrical 

 species (snake-shaped) with thousands of nuclei. Numerous 

 fissions which have started at different levels in the body are 

 still incomplete, giving the whole animal a metamerized appear- 

 ance. Of course this is but pseudo-metamerization for it is not 

 due to apical budding but rather to interrupted transverse fis- 

 sions which have started at different points along the elongated 

 body. 



The Opalinidae are an offshoot from the ancestral Ciliata at 

 a time when mitotic phenomena and the nucleus-cytoplasm rela- 

 tion were becoming disturbed. They have some of them re- 

 mained in an early stage of this condition. Others have devel- 

 oped the tendency further and have become highly multinucleate. 

 The Euciliata, rising doubtless from such pseudobinucleate 

 forms as the Protoopalinae, have passed on to a permanently 

 binucleate condition, even their gametis being binucleate, when 

 properly analyzed. The permanence of their binuclearity, once 

 established, allowed the differation of one whole nucleus for nu- 

 trition (macronucleus) and of the other whole nucleus for repro- 

 duction (micronucleus) . The Opalinidae as a whole are a group 

 in which the condition of nucleus and cytoplasm as to mitosis 



