THE GENUS TRYPANOSOMA 255 



B. The Trypanosome Nuclei. — The terms micronucleus and 

 macronucleus are frequently used to designate the trophonuclei and 

 kinetonuclei of these flagellates, but this use of the term micronucleus 

 is greatly to be deplored, since the kinetonucleus has absolutely no 

 analogy with the micronucleus of infusoria, and the binucleate con- 

 dition of the trypanosomes is to be explained upon other grounds than 

 that of the ciliates. 



The nucleus of an ordinary trypanosome is constructed upon the 

 same plan as that of simpler flagellates, and consists of a spherical 

 body of chromatin with a more or less well-defined nuclear membrane, 

 and a central division centre similar to that originally described by 

 Keuten in euglena. The nucleus, therefore, belongs to the category 

 of centronuclei, as described by Boveri ('01). Many observers have 

 been careless in describing the chromatin in such nuclei under the 

 term "chromosomes," the custom originating with Schaudinn's 

 description of the structure of Tryp. noctuae. Cytologists have repeat- 

 edly pointed out the impossibility of getting accurate cytological 

 demonstrations from poorly fixed material, and the ordinary technique 

 recommended in connection with the Giemsa staining fluid gives 

 unreliable preparations. The nucleus in particular undergoes modi- 

 fications of a well-marked character; the chromatin here appears to 

 be a fluid substance which when dried, as in a smear, coagulates in 

 irregular masses without definite structure. Moore and Breinl have 

 made similar criticisms of the so-called chromosomes of various 

 authors, and in Tryp. gambiense, Tryp. lewisi, and other forms have 

 observed nuclei of the same type as those pictured in Fig. 102, p. 260. 

 The descriptions of "chromosomes" in diflierent accounts, therefore, 

 must be taken with reserve. 



Nearly all of the subsequent observers have followed Schaudinn's 

 description of the happenings in Trypanosotna noctucc, and there is a 

 certain ground for the suspicion that the multiple and confusing 

 forms assumed by these nuclei, especially when the usual methods are 

 employed, are more easy to interpret along the lines of a path already 

 made than to be described as involution or degeneration types. Hence 

 we find in the literature all kinds of nuclei arranged in definite series as 

 illustrating "reducing divisions," or "karyogamy," or "partheno- 

 genesis," where it is more than likely that the structures thus inter- 

 preted are artefacts, or evidences of hyperplasy and degeneration. 

 The schematic figures and categorical descriptions of Schaudinn's 

 original contribution are still the most convincing of all such attempts 

 to describe the nuclear changes, and may well serve as a type, 

 although the terminology employed by this gifted and careful ob- 

 server, borrowed from the nomenclature of animal cytology, cannot 

 be employed in the same sense for these flagellates. 



The nuclear structures of Trypanosoma noduos is shown in Ficr. 



