320 SUMMARY OF CURRENT RESEARCHES RELATING TO 



The periods of depression lead to death of the culture if subjected con- 

 tinuously to the same environment. 



A cycle is a periodic rise and fall of the fission-rate, extending 

 over a varying number of " rhythms," and ending in the extinction of 

 the race unless it is " rejuvenated " by conjugation or by changed en- 

 vironment. A " rhythm " is a minor periodic rise and fall of the 

 fission-rate, due to some unknown factor in cell-metabolism, from which 

 recovery is autonomous. 



Changes in environment, e.g. treatment with extract of beef, will 

 revive the lagging functions during the descending cycle. Seasonal and 

 temperature changes have no apparent influence on the cyclical fluctua- 

 tions of vitality. Variation in temperature, however, undoubtedly 

 affects somewhat the daily rate of division — if not directly, at least 

 through the food supply. The number of generations in a cycle is not 

 at all constant, and duration in time seems of no significance. 



Periods of depression are marked by the greatly decreased fission- 

 rate, comparatively frequent pathological divisions, increased vacuolisa- 

 tion of the cytoplasm, distortion and fragmentation of the macronuclei, 

 numerical increase of the micronuclei, and reduction of the ciliary 

 apparatus. The organisms are small during periods of high reproduc- 

 tive activity, and increase in size as " degeneration " advances. Just 

 before extinction there is a secondary reduction in size. Throughout 

 the entire period of the cultures no tendency to conjugate was seen. 

 Experiments showing extreme sensitiveness to solutions of salts are 

 recorded ; the results differ at various periods in the life-cycle. Light 

 has little or no direct effect on the division-rate of Oxytriclia fallax. 



Conjugation in Infusoria.*— J. Versluys shows how partial karyo- 

 gamy or conjugation may be deduced from total karyogamy or copula- 

 tion, and considers that the former has gradually arisen from the 

 latter, mainly as a result of the increasing complication in the structure 

 of the Infusoria, and perhaps favoured also by the great independence 

 of the specialised sex nuclei. The relation between the two types is 

 clearly set forth in diagrammatic form. It is also pointed out that 

 partial karyogamy is limited in distribution, though less so than Lang 

 has supposed, which is against the view that it is primitive. 



Trophoplasmic Spherules in Ciliata.f — J. Kunstler and Ch. Gineste 

 describe under this title vesicular elements in the endoplasm of Opalina, 

 etc., which sometimes show a central nodule or internal granules, and 

 which multiply by fission, preceded by the division of the internal 

 nodule. 



New Peridinid.J — C. A. Kofoid describes from the plankton of the 

 Pacific at San Diego Station representatives of Heterodinium, a new genus 

 of Peridinidae, differing entirely from Peridinium as regards its thecal 

 plates. It belongs, with Geratium, Peridinium, and Protoceratium, to 

 the sub-family Ceratiinse, and is divisible into three sub-genera — 

 Splmrodiniam, Euheterodinium, and Platydinium. 



* Biol. Centralbl., xxvi. (1906) pp. 46-62 (2 figs.). 



t Comptes Rendus, cxli. (1905) pp. 907-8. 



% Univ. California Publications (Zoology) ii. No. 8 (1906) pp. 341-68 (3 pis.). 



