202 SUMMARY OF CURRENT RESEARCHES RELATING TO 



creeping, feeding chiefly on vegetable matter. It is spherical, with 

 numerous very fine radiate pseudopodia (asopodia), with streaming 

 granules and with axes rooted in a centrally- placed centroplast. It has 

 no stalk, no contractile vacuole, no gelatinous investment, no spicular 

 skeleton, no sharply-differentiated ectoplasm and endoplasm. The 

 nucleus is single, large, excentric, vesicular, with a large karyosome. The 

 reproduction is by equal binary fission, in which the nucleus divides by 

 mitosis, the centroplast playing the part of a centrosome. 



Entamoeba dysenteriae/"' — C. Mathis and L. Mercier discuss the 

 great differences in the dimensions of the cysts in this species. The 

 most frequent dimensions are between 12'5 /x and 14 /a, but there are 

 some of 10^ and others of 15 ji. Some have suggested that there are 

 different races within the species, but the authors are'inclined to regard 

 the differences of size as modificational fluctuations, depending on the 

 food or the like. 



Rhythms in Endomixis.t — L. L. Woodruff has met the criticism 

 that the re-organization process called endomixis may be peculiar to his 

 long-pedigreed race of Parammcium aurelia. Data from every culture 

 studied, isolated from diverse localities (as widely separated as Germany 

 and Ohio), prove that endomixis is a normal periodic phenomenon which 

 occurs in all races of the species. 



Influence of Environment on Endomixis. f—L. L. Woodruff finds 

 that general changes in the environment of different races of Paramm- 

 cium aurelia — e.g. markedly different culture media and temperatures^do 

 not permanently alter the length of the rhythm or the time between 

 successive endomictic periods which is characteristic of the species. 

 Sudden marked changes in the normal culture conditions may initially 

 hasten the endomixis, but this is soon compensated for. There is a 

 remarkable synchronism of the endomictic process in all the races bred 

 simultaneously, regardless of the environmental conditions. The length 

 of the rhythm and the rhythmic periods are synchronous. But the 

 " generation-periodicity " — i.e. the number of cell divisions between one 

 occurrence of endomixis and the next— may be modified to a considerable 

 extent by the culture conditions which lower the division-rate. The 

 cessation of endomixis in the experiments was always followed, usually 

 within a rhythm or two, by the death of the culture involved. Every- 

 thing points to the conclusion that a periodic occurrence of the definitive 

 endomictic phenomena is a sine qua no7i for the continued life of the 

 race. 



Genus Loxodes.§ — E. Penard discusses some of the peculiarities of 

 this remarkable Ciliate. In reference to L. rostrum, he describes, for 

 instance, the external envelope, the buccal area, the attaching filaments, 

 the vacuolation of the cytoplasm, the twenty to thirty nuclei, the abrupt 



♦ C.R. Soc. Biol. Paris, Ixix. (1917) pp. 791-3. 

 t Biol. Bulletin, xxxiii. (1917) pp. 51-6. 

 ; Biol. Bulletin, xxxiii. (1917) pp. 437-62 (12 figs.). 

 § Rev. Suisse Zool., xxv. (1917) pp. 453-89 (12 figs.). 



