ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 313 



solation is regarded as the cause of the extension of a pseudopodium ; 

 coagulation or gelation as the cause of the withdrawal of pseudopodia ; 

 and of active contraction. This theory is an extension of one previously 

 iidvanced by Rhumbler. J. A. T. 



Reactions of Pelomyxa to Food. — AY. A. Kepner and J. Graham 

 Edwards {Journ. Exper. Zool. 1917, 24, 381-407, 14 figs.) find two 

 kinds of reactions, according as the objects engulfed are capable or 

 incapable of retreat. The food includes plants and animals, and varies 

 in size from Nematodes to very minute Infusorians. The paths of 

 possible retreat of motile organisms present a wide range of variability, 

 and the details of the amoeba's reactions cannot be predicted. No 

 hypothesis yet advanced to explain the movement of Rhizopods can be 

 applied to the solution of the problem of the movement of Pelonnjxa in 

 relation to the food-bodies. J. A. T. 



Entamoeba histolytica and Entamoeba ranarum.— Clifford 

 DoBELL {Parasitology, 1918, 10, 294-310) has made numerous experi- 

 ments in the attempt to infect tadpoles with the human Entammha 

 histolytiea, but it seems that the cysts, when ingested, pass unchanged 

 through the intestine, without undergoing any development. This 

 indicates the conclusion that the two species, in spite of close resemblance, 

 are somehow distinct, and that the frog, in all probability, is not a 

 *' reservoir " of human amoebic dysentery. J. A. T. 



Races of Entamoeba histolytica. — Clifford DoBELLand Margaret 

 W. Jepps {Parasitology, 1918, 10, 320-51, 1 pL, 7 figs.) find that 

 Entamaba histolytica Schaudinn (vel E. dysenterise Councilman and 

 Lafleur) is a collective species, comprising a number (five) of distinct 

 races, strains, or pure lines, distinguishable from one another by the 

 size of the cysts which they produce. These races remain constant in 

 character within a given host ; and the dimensions of the cysts are not 

 determined by the action of the host upon the parasite, since two 

 different races may co-exist side by side in the same host. Since cysts 

 of E. histolytica may be found with all diameters from about 5ju, to 

 20 /A — a range overlapping or covering the dimensions of the cysts of 

 the harmless intestinal amcebre {E. coli and E. nana) and of other cysts 

 and cyst-like bodies in human fteces— it is of considerable practical 

 importance to recognize and distinguish the diverse races of the collective 

 species in question. J- A. T. 



New Amoeba from Man. — Margaret W. Jepps and Clifford 

 DoBELL {Parasitology, 1918, 10, 352-G7, 1 pi.) describe Dientammha 

 fragilis g. et sp. n., a very small amoeba from the human intestine. The 

 diameter when rounded is about 3-5 /x to 12 /a, averaging about 9/x; 

 the cytoplasm is differentiated into ectoplasm and endoplasm ; the 

 pseudopodia are flattened, hyaline, and leaf-like, usually few, with 

 irregularly dentate margins ; the progression is snail-like ; there are no 

 contractile vacuoles. There are typically two nuclei, averaging about 

 2 fx.. Each possesses a large central karyosome surrounded by a clear 

 zone containing no peripheral chromatin and limited externally by a 

 very delicate achromatic nuclear membrane. The organism probably 



Y 



