THE OPALIXID CIIJATE IXri'S;)r.IAXS, 267 



The definite localization of the excretory vacuole and its pore in 

 Opalinids might seem an advance over conditions in the Plasino- 

 droma. but it has been shown that even in Amoeba the excretory' 

 vacuole and its pore are in constant relation to a localized portion 

 of the plasma and pellicle (Metcalf, 1910), 



The locomotor organs are cilia similar to the less modified of the 

 cilia among the Euciliata, and they are inserted in longitudinal, 

 spiral, pellicular grooves, as among the holotrichous Euciliata, the 

 basal granules forming lines beneath these grooves. This is a feature 

 of decided resemblance to the Euciliata. Among the Plasmodroma. 

 the genus Trichonympha shows similar longitudinal, spiral lines of 

 "flagella," but these instead of being set along the bottoms of 

 pellicular grooves, are set along the crests of well defined, longitu- 

 dinal, spiral ridges. The flagella themselves, \Ai\\ their basal 

 granules, seem comparable to the cilia of Opalinidae and holotri- 

 chous Euciliates. 



The kinetic structures in the Opalinidae are developed only in 

 connection with the cilia. They consist of rows of basal granules, 

 one for each cilium, connected longitudinally by minute fibrillae, 

 and also apparently connected laterally from row to row. Among the 

 Euciliata Holotricha we find a somewhat similar condition. Nothing 

 quite like this is known among the Plasmodroma. The nearest ap- 

 proach is in the genus TnchonyTrupha^ but in this genus there is a 

 distinct kinetic center at the anterior end of the body, much as in 

 Noctiluca. The subpellicular kinetic fibrillae are more developed in 

 Triehonytnpha than in the Opalinidae. The Opalinidae have no 

 kinetic center or centers, not even a centrosome within the nucleus. 

 In respect to the character of their kinetic structures they most re- 

 semble the Euciliata Holotricha, but lack the centrosome which is 

 observed in the latter during the mitosis of the micronucleus.-" 



There are several striking features in the nuclear conditions of the 

 Opalinidae : 1, the presence regularly of tAvo or more nuclei in one 

 body; 2, the exact resemblance of these nuclei to one another; 3, 

 the al>sence of a nuclear (or any other) centrosome: 4. the permanent 

 persistence of the nuclear membrane, a rather usual Protozoan char- 

 acter among both Plasmodroma and Euciliata ; 5, the presence of two 

 distinct sets of chromosomes in each nucleus, each Avith its own set 

 of chromatic fibrillae; 6, the apparent individuality of chromo- 

 somes of each set, at least in the Protoopalinac ; 7, the absorbing 

 of most or all of the inacrochromatin before sexual union, with 

 its consequent interpretation as trophic in contrast with the re- 

 productive microchromatin: 8, the formation of a threefold 

 chromatic spindle from a, the macrochromatin fibrillae, Z/, 



^Recent studies by Rees (1922) have shown that Paramecium has a well-developed 

 neuromuscular center near the anterior end of the buccal groove. It is possible that 

 proper fixing and staining would demonstrate a neuromuscular center in Opalinids. 



