THE GENUS TRYPANOSOMA 257 



the early hypothesis of Balfour and Minot that the nucleus of the 

 primordial egg or sperm cell contains both kinds of sex chromatin, 

 the opposite kind being eliminated by the reducing diyisions of each 

 sex. It may be noted in this connection that while modern cytology 

 has brilliantly confirmed the essence of this theory, it is not at all in 

 the way supposed by the early speculators, nor at all in the way out- 

 lined by Schaudinn in this trypanosome (see Wilson, Steyens, and 

 others on sex chromosomes in insects). 



The kinetonucleus yaries greatly in size, from a mere granule, as in 

 Tryp. gamhiense, to a large body equal to, or larger than, the nucleus 

 (as in Trypmioplasma horreli) ; the great majority of forms present no 

 such structures as described by Schaudinn, the kinetonucleus usually 

 being homogeneous and dense in appearance; Robertson ('07), how- 

 ever, finds "chromatic" thickenings in Tryp. raioe which she interprets 

 as equivalent to the chromatin of Schaudinn's form. 



The relative positions of kinetonucleus and nucleus are used by 

 many observers as of sufficient importance to justify specific distinc- 

 tions; this was considered of more importance formerly than it is 

 today; indeed, at the present time no conclusions as to taxonomy can 

 be drawn from such relations. Novy, Minchin, Robertson, and a 

 host of others have shown that in the same species the kinetonucleus 

 may be anterior, lateral, or posterior to the nucleus (Fig. 100, p. 249). 



C. Form Changes of Trypanosomes. — The variations in the 

 relative position and sizes of the nuclei accompany the greatest variety 

 of form changes in the body as a whole and next to the ameboid 

 forms, which after all have a certain constancy in their form changes, 

 these trypanosomes are perhaps the most variable of protozoa. They 

 seem to be highly susceptible to the conditions surrounding them. 

 "I am convinced," says Minchin, "that the appearance, and even the 

 structure, of trypanosomes may be greatly affected by the condition of 

 their hosts" (190S, p. 17S). If slight changes in the blood of verte- 

 brates can bring about such marked changes in structure of the para- 

 sites, it is obvious that the much greater change in external conditions, 

 when transferred from the vascular system, especially of mammals, 

 to the relatively cold environment of an insect's digestive tract, should 

 be the cause of even greater changes. The modifications brought 

 about by these several different conditions have been variously inter- 

 preted as sexual differences, as resting phases, degeneration phases, 

 and the like, while so-called latent bodies and encysted forms have 

 been found in some cases. 



Size differences were first brought into prominence by Schaudinn 

 in connection with the rapid multiplication of Tryp. ziemanni of the 

 owl, where, he states, "as a result of the rapid multiplication the indif- 

 ferent spirochetes (trypanosomes) become remarkably small; indeed, 

 I have found forms which are so unmeasurably fine that they can be 

 17 



