STUDIES IN THE LIFE-HISTORY OF EUGLENA. 349 



Trichonympha, brought about by a pairing of single chromosomes 

 in the prophase. He suggests the possibility of a pregametic 

 doubling of chromosomes in Protozoa such as occurs in the 

 Metazoa, but does not consider this to be the most plausible 

 explanation of the observed facts. 



Stevens describes the association of chromosomes in pairs 

 during the vegetative stages of Boveria subcylindrica. The 

 significance of this apparent reduction in vegetative mitosis is 

 problematical and the subject requires much more work before a 

 correct interpretation and correlation can be made. In Uroleptus 

 mobilis Calkins finds eight chromosomes which unite in four pairs 

 during the first maturation division, the pairs splitting at the 

 second maturation division so that the daughter nuclei have four 

 single chromosomes. He concludes that this is undoubted 

 synapsis arid reduction. 



Tschenzoff describes a telophasic split in Euglena viridis, which 

 doubles the number of chromosomes entering the resting vege- 

 tative stage. Such a precocious split has not been observed in 

 Euglena agilis, although the double appearance of the chromatin 

 masses may be indicative of such a process. On the other hand, 

 a definite longitudinal split has been observed in the prophase. 



It is not known what changes take place in the nucleus during 

 the encystment in Euglena, but it is entirely possible that some 

 phenomena will be found here to throw light on the apparently 

 paired arrangement of the chromatin masses. 



Metaphase. Tschenzoff describes in the metaphase, a sepa- 

 ration of daughter chromosomes formed by a splitting in the 

 telophase of the preceding generation. He states that the 

 elements may be seen paired on the spindle at this stage and then 

 separating without further split. Structures may be observed in 

 Euglena agilis which might easily be interpreted in this manner 

 but which show on critical examination an entirely different 

 situation. The network of chromatin in the resting nucleus 

 becomes enlarged at the nodes or at the points where the chro- 

 matin masses are fusing to form chromosomes. This increase in 

 bulk of chromatin does not seem to be compensated for by a 

 corresponding increase in size of the nucleus. Since the nuclear 

 membrane remains intact during the entire process of division the 

 23 



