ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 209 



result of conjugation. This optimum is subject to change by environ- 

 mental conditions, being increased, for example, by heat. It also 

 appears that rejuvenescence may follow encystment and parthenogenesis 

 when no nuclear interchange has occurred. In some cases the re- 

 juvenating effect of parthenogenesis was even greater than that of 

 conjugation. Parthenogenesis through encystment seems to be am 

 attribute of high vitality, and the ability to encyst is apparently lost 

 at an early date. The condition of physiological depression is ac- 

 companied by structural changes, which are described in detail. In 

 conjugation the most significant phenomenon is the granular disin- 

 tegration of the old macronuclei and the absorption of relatively large 

 quantities of nuclear substance in the cytoplasm. The same is true of 

 encystment and in division — there is re-organization of the cytoplasm. 



J. A. T. 



Periodicity in Photic Responses of a Euglenoid. — S. 0. Mast 

 {^Proc. Amer. Soc. Zool. in Anat. Record, 1920, 17, 345). In some 

 organisms — eg. Convohita — changes of movement continue for some 

 time in the absen(;e of the environmental conditions to which they were 

 formerly related (the tides in the case mentioned). Like many of the 

 Euglenoids, Septocinclis texta responds very definitely to light. If kept 

 in total darkness and tested from time to time in an illumination of 

 proper intensity, it is positive from early morning to about 1 p.m. It 

 then becomes negative, and remains so till 8 or 9 p.m., when it becomes 

 positive again until the following afternoon. Thus in the absence of 

 light, for at least three days, there appears to be in its physiological 

 processes a periodicity w^hich is normally associated with alternation 

 between day and night, and determines whether its orientation to light 

 is positive or negative. J. A. T. 



Adaptation to Light in Euglena variabilis. — S. 0. Mast {Proc. 

 Amer. Soc. Zool. in Anat. Record^ 1920, 17, 346). Euglena becomes 

 rapidly adapted to any given illumination, and if adapted to low illumi- 

 nation or darkness it tends to be negative in strong and positive in 

 weak light, and to aggregate in moderate illumination. If adapted to 

 high illumination, it tends to be positive in strong and negative in weak 

 light, and to aggregate in very high and very low illumination. J. A. T. 



Trichomonas of Guinea-Pig. — Edouaed Chatton {C. R. Soc. Biol., 

 1920, 83, 69-72). An account of attempts to secure a pure culture of 

 a species of Trichomonas which is often very abundant in the caecum of 

 the guinea-pig. It lives well in ordinary bouillon to which blood is 

 added, but it was not found practicable to get rid of four kinds of 

 associated bacteria. The flagella are markedly alkalinophilous. In the 

 culture the recurrent flagellum of Trichomonas separates from the body, 

 suppressing the undulating membrane. When inoculated into the peri- 

 toneum of the guinea-pig there is a reappearance of the undulating 

 membrane. In different media there are different surface-tension 

 conditions which may influence the structure ; there may also be an 

 influence from specific substances. The transformation shows how close 

 the relationship is between Trichomonas and Trichomastix. J. A. T. 



P 



