32 BULLETIlSr 120, UNITED STATES NATIONAL, MUSEUM. 



and longitudinal as well as transverse fission of the body follows. I see no 

 difficulty in its occurring in P. primordialis. If Awerinzew means merely that 

 longitudinal fission does not occur because he failed to find it among the 

 individuals in the single infection he observed, I would suggest that this is 

 not unnatural. I have comparatively seldom seen longitudinal fission in 

 freshly taken material, though I have studied material from many hundreds 

 of infections of numerous species. I have however found many individuals 

 with the beginnings of the longitudinal splitting showing as a slight inden- 

 tation of the contour of the anterior end of the body, or appearing in a widen- 

 ing of the whole body. A slightly diagonal orienting of the two nuclei, one 

 to the left, the other to the right, frequently accompanies the earliest stages 

 of longitudinal fission and may be recognized by one familiar with the phe- 

 nomena of fission in these animals.] 



From the standpoint of the individuality hypothesis, which recognizes the 

 several chromosomes as autonomous life-entities [" Lebenseinheitcn "] the 

 described case of a persistent existence of independent chromosomes, accord- 

 ing to my conception, is most reasonable for the organism, for the organism 

 thereby succeeds during the vegetative stage of the nucleus in avoiding the 

 complicated progressive series of phenomena which involves a change in the 

 nuclear structure and might well lead to a loss of independence of the chro- 

 mosomes. [This sentence I have interpreted instead of translating. In Ger- 

 man it reads : — " Vom Standpunkt der Individualitatshypothese, die die ein- 

 zelnen Chromosomen als autonome Lebenseinheitcn anerkennt, ist die be- 

 schreibene Fall einer bestandigen Existenz von selbststandigen Chromosomen, 

 meiner meinung nach, der fiir den Organismus am meisten rationale, da es 

 ihm dadurch gelingt, wiihrend des vegetativen Stadiums des Kernes die 

 komplizierten Frogresse zu vermeiden, welche zu einer abilnderung der Kern- 

 struktur und zum Verlust der Selbststiindigkeit der Chromosomen fiihrt." In 

 Protoopalina intestinalis, P. caudata and numerous other species whose nuclei, 

 like those of P. primordialis rest in a midmitotic condition, the nuclei do go 

 through a reticulate stage, which, however, is not prolonged. It would re- 

 quire detailed study of the nuclear cycle in P. primordialis to determine 

 whether it does or does not have a similar transient reticulate stage. At any 

 rate, the independence of the chromosomes probably results not so much from 

 space relations, as Awerinzew implies, as it does from physico-chemical condi- 

 tions.] 



Since forms with nuclei constantly in the mitotic condition have been 

 wholly unknown," I consider the species of Opalina discovered by me to be 

 new and I designate it Opalina primordialis. On the basis of a series of 

 peculiarities which are possessed by different Opalinae, among which the 

 nuclear structure is in part to be included, these animals must be separated to 

 a wholly distinct group of cell-like organisms (=Protozoa), which possibly is 

 related to the typical ciliate infusoria, but which can not be included merely as 

 a separate family of the order Holotricha. 



Awerinzew's description has been quoted nearly in full. As we 

 go further with our description of the Protoopalinas we will see 

 that their most salient character is the general prevalence among 

 them of peculiar mitotic conditions such as have been described 

 first for P. mitotica and later by Awerinzew for P. primordialis. 



^ Conditions similar to those here described by Awerinzew were previously described by 

 Metcalf ( 1912) for Protoopalina mitotica, as Awerinzew mentions above. 



