I 



428 metcalf: opalina and the ciliate infusoria 



dozen new species of Opalinidae and necessitates revision of the 

 taxonomy in the family and in the Cihata. The new forms en- 

 able us to gain a comprehensve knowledge of the plan of speci- 

 ation among the Opalinidae and the conditions revealed in this 

 family throw light upon the origin of the Ciliata. 



The family Opalinidae comprises properly but two genera — 

 Protoopalina (new genus) and Opalina. Protoopalina has one 

 nucleus or in most species two nuclei. Their nuclei contain two 

 distinct sets of large, flat, superficial chromosomes of constant 

 and characteristic number in each species, and another more 

 central set composed of the same number (in the species thus far 

 studied) of slender chromosomes each consisting of a linear ag- 

 gregate of granules much as in Paramecium, except that the 

 granules are much coarser in these large nuclei. In mitosis the 

 daughter nuclei each receive one-half of each chromosome of 

 each sort (massive and granular). 



Opalina has many nuclei (4 to several thousand). Each nu- 

 cleus contains some (not many) large, flat, superficial chromatin 

 masses of varying number in the different nuclei in the body and 

 also numerous, more central, slender chromosomes, each a linear 

 aggregate of granules. It is probable that these linear chromo- 

 somes are of constant number for each species, but they ara too 

 numerous for easy study. In the genus Opalina the granular 

 chromosomes seem to be as carefully and regularly divided as 

 they are in Protoopalina, but the larger masses of chromatin are 

 irregularly divided in mitosis, and some of them may occasionally 

 remain undivided, passing bodily without division into one of 

 the daughter nuclei. 



In both Opalina and Protoopalina the massive chromosomes 

 are trophic, the granular chromosomes reproductive. Each 

 nucleus contains both kinds of chromatin and there is no special- 

 ization, as in the higher Ciliata, of whole nuclei as trophic and 

 other whole nuclei as reproductive. 



The most characteristic feature of the higher Ciliata is the 

 possession by each individual of a large trophic nucleus and 

 another minute reproductive nucleus. The absence of this char- 

 acter in the Opalinidae justifies placing them as an archaic group, 

 Protociliata, and classing the rest of the Ciliata as Euciliata.. 



