62 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Protozoa. 



Conjugation and Encystation in Didinium nasutum.* — S. 0. Mast 



has studied various groups of pure lines of this Ciliate, between April, 

 1910, and May, 11)14. During this time there were produced without, 

 conjugation an average of 164G generations per line, and without encyst- 

 ment an average of 1035 generations per line. At the close the stock 

 was very weak, but it did not die out. It is not likely that either 

 conjugation or encystment is necessary for continued existence in this. 

 Infusorian. 



From time to time new groups of lines were started from old ones,. 

 some after conjugation, others after encystment, and still others without 

 either conjugation or encystment. There were, consequently, continu- 

 ously present a number of groups of lines which differed in the number 

 of generations produced since conjugation or encystment had occurred. 



The rate of fission varied greatly throughout the experiment, owing 

 largely to changes in temperature, but at any given time there was- 

 approximate uniformity in the fission-rate (and also in the death-rate) in 

 all the groups of hues regardless of the distance removed from conjuga- 

 tion or encystment. There was, therefore, no evidence indicating the 

 presence of cycles related to these processes. 



There was no evidence that conjugation or encystment has any 

 appreciable effect on death-rate, fission-rate, or variation in fission -rate. 

 This would indicate that neither conjugation nor encystment is a re- 

 juvenating process, at least not in the sense in which Calkins uses the 

 term. 



In one of the groups of lines, 721 generations after conjugation and 

 197 generations after encystment, some of the offspring suddenly began 

 to divide more rapidly than others. The difference in the rate of 

 fission in these two sets of individuals remained fairly constant 

 throughout the remainder of the experiment, 315 days. During this 

 time one set produced an average of 838 generations per line, 2| per 

 day ; the other, an average of 634 generations per line, 2 per day. 



Life-history of Ceratomyxa herouardi.f — Jivoin Georgevitch gives 

 an account of this interesting Myxosporidium which he found in the 

 gall-bladder of Box salpa. Ripe spores from another host enter the 

 gall-bladder from the food canal. The spores, which have lost their 

 capsular filaments (used in their pilgrimage), liberate the sporoplasm 

 which is binucleate. The sporoplasm emits a pseudopodium ; the two 

 nuclei unite completely, forming a zygote or pansporoblast which fixes 

 itself by pseudopodia to the wall of the gall-bladder. The nucleus 

 divides twice, forming a large vegetative nucleus and two smaller germi- 

 native nuclei. 



The pansporoblast may exhibit schizogony, or schizogony with 

 repeated divisions of the germinative nuclei, or it may exhibit direct 

 sporulation. In a very complicated fashion, of which the author gives 

 an indispensable diagrammatic illustration, there is an alteration of a 

 sexual phase and numerous asexual phases. 



* Journ. Exper. Zool., xxiii. (1917) pp. 335-59. 



t Arch. Zool. Exp^r., Ivi. (1917) pp. 375-99 (2 plf. and 3 figs.). 



