PROTOZOAN NUCLEI. 385 



Chilomonas cylijidrica Ehg. (Plate XXXV, Figs. 8, 9, 10.) 

 This very common flagellate is characterized by the buccal 

 depression typical of the family CryptomonidcX, by two equal 

 flagella, by an oesophagus-tract in the endoplasm, by absence of 

 chromatophores, and in most cases, by the absence of plastids. 

 The absence of cytoplasmic intra-cellular substances makes 

 Chilomonas particularly favorable for nuclear study as well as 

 for the study of cytoplasmic structure. The nucleus is a con- 

 spicuous body in the lower half of the cell just below the mid- 

 dle line. It is always irregular in outline, the irregularity being 

 due to prolongations of its substance, like pseudopodia, into the 

 adjacent protoplasm. We again find the granular chromatin 

 and the intra-nuclear deeply-staining body. In this case, there 

 is, in all probability, no nuclear membrane, and from the vari- 

 ous shapes of the nuclei in different individuals it is inferred 

 that the chromatin granules may become more or less scattered, 

 although remaining in the vicinity of the central body. During 

 division of the cell the chromatin becomes closely aggregated 

 around the central body which divides first, the chromatin gran- 

 ules, as in Eugloia, separating later into two equal portions. 

 Division here is not as complicated, however, as in Engicna, for 

 the chromatin granules do not fuse into distinct rods or chromo- 

 somes as in the latter form (Figs. 9 and 10). 



Trachelomonas. Several species of Trachelomonas were ex- 

 amined and in all cases the nuclei were of the same type as 

 those already described. Among the most noteworthy were 

 the nuclei of T. lagcnclla, T. volvocina and T. Jiispida. The 

 simplest of these was found in T. lagcnclla (Fig. 1 1) where, as 

 in Chilomonas, it consists of an irregular mass of chromatin 

 granules surrounding a central body. No nuclear membrane 

 was seen, although the protoplasmic structure was plainly ap- 

 parent. Compared with the entire nucleus the central body in 

 this case is quite small. 



Two varieties of T. hispida, which for convenience I shall 

 characterize as variety A, and variety B present two distinct 

 phases of nuclear arrangement. The two forms differ in other 

 respects ; variety A is smaller, has no collar, has a compar- 



