230 SUMMARY OF CURRENT RESEARCHES. 



usually lie close to the epithelial walls. There is absorption of food 

 through the epimerite as well as by the general surface. 



Normal salt solution is the best artificial medium in which to study 

 the movements of Gregarines. Locomotion is effected by means of a 

 progressive, gliding movement, with no apparent localized motion of 

 the body. In Leidyana erratica progression takes place at the average 

 rate of 0*8 micron per second. In artificial media there are formed 

 gelatinous threads at the posterior end of the deutomerite. These threads 

 do not occur in a freshly-made mount ; they may be seen with a high 

 power and a minimum amount of light in a mount which has been 

 made for some time ; they may be demonstrated with carmin particles 

 in suspension. 



The animal probably moves by imperceptible vertical movements 

 of the myonemes of the side which is ventral at the time, and upon a 

 surface whose friction is caused by an exudation of slime from the body 

 of the parasite. This mucus is secreted by the body and exudes through 

 pores between the longitudinal ridges in the epicyte or delicate ex- 

 ternal ectoplasm. The mucus passes backwards along the longitudinal 

 ridges to the posterior end, and is discharged as a waste product in 

 the form of broken threads or strands. The anterior half of the 

 deutomerite is the region chiefly involved in bending movement. The 

 protomerite is incapable of independent bending movement. The 

 normal object of contortion is the formation of cysts. 



Evolution among Protozoa.* — R. D. Glreenaway discusses some 

 structures the evolution of which cannot, he thinks, be readily inter- 

 preted in terms of Natural Selection. The Thecolobosa like Dlfflugia 

 and Arcdla live along with naked Amoebse which are more numerous 

 than they ; poly-flagellates live in the same conditions of life as mono- 

 flagellates ; the highly specialized Ciliata live side by side with 

 flagellates (which, being less " fit," should on the Selection Theory, as 

 conceived by the author, have become extinct long since). Similarly, 

 extremely minute and the relative gigantic Ciliata, Bodo and Traehelius, 

 rub shoulders in every environment,- the excellence of the springing 

 apparatus in Halteria, or the trophic cilia of Bursaria, or the setose 

 processes of Euplotes, have arisen without any sign of extinction on the 

 part of less well-endowed neighbours. It is the recorder's task simply 

 to illustrate the point of Mr. Greenaway's criticism, but it should be 

 noted that the difficulty raised was familiar to Darwin, and arises from 

 an inadequate conception of the theory of Natural Selection. 



* Zoologist, XX, (1916) pp. 303-11. 



