1914] Sharp: Diplodinium ecaudatum 71 



in the macronucleus in its preparation for and during division will 

 be described in a subsequent paper. 



Micronucleus. — The micronucleus may be clearly distinguished 

 even in the living non-stained animals. Here it appears, by trans- 

 mitted light, as a shining little body situated in a depression on the 

 dorsal side of the macronucleus about midway between the anterior 

 and posterior extremities. In the living condition it appears finely 

 granular in structure and refracts light more strongly than does the 

 macronucleus. In the stained preparations the micronucleus {mic, pi. 

 3, figs. 1, 2; pi. 4, figs. 3, 5; pi. 7, figs. 29, 33), is seen to be oblately 

 spheroidal in shape, somewhat flattened dorso-ventrally, with its long 

 axis placed longitudinally. The micronucleus, like the macronucleus, 

 is encapsuled by a clear, well-defined membrane, between which and 

 the nuclear substance is a structureless, clear space. The capsule of 

 the micronucleus is firmly held in position by suspensory fibers (susp. 

 f., pi. 4, fig. 3), which appear to arise from the nuclear membrane of 

 the macronucleus above and below the depression for the micronucleus 

 and its capsule. After iron-alum haematoxylin stain the micronucleus 

 substance shows blue-black. After Mallory's connective tissue stain 

 the micronucleus shows bright red. This is especially interesting when 

 considered in connection with the fact that the micronucleus, together 

 with some peculiar masses and fibers which are to be described later, 

 takes this stain in the same intensity and they are the only structures 

 which do show this peculiar, bright red. Since these peculiar masses 

 and fibers are intimately connected with the organs of locomotion, and 

 since they and the micronucleus invariably take the same stains in 

 the same intensity it would seem that some relationship (chemical at 

 least) must exist between the motor apparatus and the micronucleus, 

 in which case the micronucleus might properly be termed a kineto- 

 nucleus. This belief is strengthened by the fact that many cases have 

 been observed by me in Diplodinium in which the macronucleus was 

 engaged in dividing up into definite chromosomes, a function which 

 in ciliates, except in Opalina, is generally supposed to be limited ex- 

 clusively to the micronucleus. In other words, it appears that the 

 macronucleus here may be analogous to the trophonucleus of try- 

 panosomes and so the question is raised as to whether or not it might 

 be held to contain the so-called "generative chromatin." This phe- 

 nomenon will receive further consideration in my paper on conjuga- 

 tion and reproduction in Diplodinium ecaudatum. The granules of 

 the micronucleus are too small and too numerous to permit even an 



