306 SUMMAKY OF CLfERENT KESEAKCHES RELATING TO 



round it like an indiarubber bag. A small DkUnium will thus swallow 

 a Paramacium six times its size, and on several occasions one was seen 

 to attack and swallow a conjugating pair. The walls of the captor were 

 usually equal to surrounding the victim, but more than one individual 

 was seen to explode as a consequence of its too hearty meal. The 

 proboscis is a conical projection in the centre of the anterior end. It 

 is supported by a dense layer of trichites anchored deep in the proto- 

 plasm. In the centre of the conical proboscis is a column of protoplasm 

 somewhat denser than the rest of the endoplasm. This is the " seizing- 

 organ " which fastens on the prey and draws it into the body of the 

 captor. Granules liberated from the seizing-organ when it penetrates 

 the cortex of its victim are apparently the cause of the paralysis. 



The history of the race for six months is given, but details of 

 encystment and conjugation are reserved for a later paper. The 

 general conclusion in regard to encystment in ciliates is that it serves 

 a threefold purpose : For protection against adverse conditions of 

 environment, for reproduction, and for reorganization, which has to do 

 with the internal processes of the cell. In DkUnium there is no 

 encystment for purposes of reproduction, but it is frequent for purposes 

 of protection, and periodic for reorganization. In the latter case the 

 approach of encystment can be^ predicted very often from the reduced 

 activity in feeding and dividing, two to four days in advance. Fresh 

 w'ater added does not bring such individuals out of their cyst until at 

 least five days have elapsed. 



Mitosis in Trichomonad Flagellates.* — C. A. Kofoid and Olive 

 Swezy publish the results of a long series of observations dealing with 

 the processes of binary and multiple fission and the accompanying 

 phenomena of mitosis in trichomonad flagellate Protozoans parasitic in 

 the digestive tract of Vertebrates. The processes of mitosis and 

 multiple fission are carried out during periods of great amoeboid 

 activity of these paa'asites in the mucus of the intestine. Mitosis is 

 pro-mitotic with nuclear membrane intact throughout the period of 

 division, with nuclear separation by constriction simulating amitosis. 

 It is, however, essentially mitotic with extra-nuclear division-centres, 

 intra-nuclear spindle fibres, and chromosome organization out of a 

 chromatin network and skein. The chromosomes are definite in 

 number and are differentiated in form and size, and in behaviour. 

 The chromosomes appear to be split longitudinally prior to their 

 arrangement in the equatorial plate, and seem to slip into an end-to-end 

 position in this plate, or to show a transverse constriction. The 

 extra-nuclear organelles all share in the process of mitosis. The 

 blepharoplast from which flagella, rhizoplast, chromatic margin and 

 basal rod, and axostyle all take their origin, contains the division- 

 centre. It divides into two bodies which go to the two poles of the 

 fusiform mitotic nucleus spinning out the deeply-staining extra-nuclear 

 paradesmose (central spindle) between them. The daughter blepharo- 

 plasts may each divide in the polar position into an axial centrosome, 



- * Proc. Amer. Acad. Arts and Sci., Ivi. (1915) pp. 290-364 (8 pis. and 7 figs.). 



