No. G34] SHORTER ARTICLES AND DISCUSSION 455 



found on these slides. Several amicronucleate individuals con- 

 tain three distended contractile vacuoles. All the micronucleate 

 individuals contain only two. There is reason to believe that 

 these slides were made from the same cultures from which Doc- 

 tor Jacobs obtained his animals for experimentation. There- 

 fore these slides also indicate the identity of the two races. Ap- 

 parently both the extra vacuoles and the absence of a micro- 

 nucleus were characters present before the heat experiments 

 referred to. 



Throughout the entire history of the cultures observed the 

 lightly stained, comparatively large, very irregular, and ex- 

 panded macronucleus is characteristic of the race. Under poor 

 cultural conditions animals with regular nuclei are few in num- 

 ber and these nuclei are. usually oval in shape and proportion- 

 ately larger, more lightly stained than others and often blending 

 with the cytoplasm. Under the same conditions condensations 

 of the chromatin material are of frequent occurrence and consist 

 of three types: (a) small or large tongues of chromatin, com- 

 pact and darkly stained throughout or only around the edges, 

 usually lying in a concavity of the macronucleus, (&) small, cir- 

 cular, dense masses of chromatin, usually flattened and near the 

 surface of the macronucleus, (c) bar-shaped condensations, many 

 times longer than broad, ranging from very loose aggregations 

 of granules to very compact masses. 



In the early part of the work the writer often experienced 

 difficulty in deciding whether or not a micronucleus was present 

 because macronuclear condensations frequently resembled micro- 

 nuclei. But after observing many specimens they were easily 

 distinguishable since neither condensations, lobes, nor detached 

 portions of the macronucleus possessed the detailed structure 

 typical of a micronucleus. They could always he identified on 

 very careful examination as portions of the macronucleus by 

 the arrangement of the chromatin. It is possible that Hance 

 may have seen macronuclear condensations resembling a micro- 

 nucleus or small detached portions of the macronucleus which 



Other differences between the nuclei of micronucleate and 

 amicronucleate animals were noticed. The macronucleus of the 

 wild, micronucleate races is compact, comparatively small and 

 darkly stained with a distinct concavity for the micronucleus. 

 The nucleus of the amicronucleate race is large, expanded, and 

 light ly staining. 



