38 



SCIENCE-GOSSIP. 



contractile vacuole is situated near the hinder 

 end ; it is sometimes single, sometimes subdivided 

 into three or four smaller vacuoles. The nucleus 

 is situated subcentrally. The protoplasm is some- 

 what granular. This animal is the largest repre- 

 sentative of the genus Monas, being from 40 to 70 

 microns in length. It was discovered by Stein, 

 and called by him Cercomoiias ramuiosa. As, how- 

 ever, the genus Cercoiiionas is characterized by a 

 caudal filament which is not present in the species 

 in question, it was transferred by Saville Kent to 

 the genus in which it now stands. 



Its habitat is similar to that of the preceding 

 species. 



Monas viica Miiller, is roughly oval in shape, but 

 like all the other species of the genus it is by no 

 means constant in this respect. The protoplasm 

 is transparent and coarsely granular. It occurs in 

 fresh water, and swims in a slow and oscillating 

 manner, like one which has lost its way. The 

 length of the b jdy is about 15 microns. 



the body itself. This sometimes takes the form 

 of a fine filament, scarcely greater in diameter 

 than the flagellum itself; sometimes it is somewhat 

 thicker, and may even take the form of an elongate 

 transparent tail. Dujardin says that it is capable 

 of an undulatory movement. The body of C. crassi- 

 cauda is elongate ovate in shape, and about two and 

 a-half times as long as broad. The caudal filament 

 is usually very thick at the base, and tapers to a 

 fine point at its distal end. In length it is about 

 equal to the body. The anterior flagellum is much 

 finer and longer than the caudal filament. The 

 protoplasm is granular. There are usually two 

 or three contractile vacuoles present, which are 

 situated near the anterior end. The nucleus is 

 subcentral in position. The length of the body 

 is about 24 microns. 



This animal may be met with in fresh water and 

 vegetable infusions. 



Oikomonas sieinii Saville Kent. — The genus 

 Oikomonas agrees structurally very closely with 



Fig. 15. — Cercomonas 

 crassicatida ( x 600). 



Fig. 16. — Oikomonas 

 stcinii { x 750). 



Fig. 17. — Heteromita ovata ( x 600). 

 /;•, tractellum ; gitb, gubernaculum ; cv, contractile vacuole ; «, nucleus. 



Monas viridis Dujardin. — The body of this 

 animal is spherical. One half is green, the other 

 is colourless and transparent. The flagellum is long 

 and slender. The length of the animal is 8 to 

 10 microns. It occurs in fresh water, and is social 

 in habits. About the validity of the species is some 

 considerable doubt. Dujardin says he found a 

 drawing of it in his note-book, but that he would 

 have to see the animal itself again to make quite 

 certain of it. De Fromentel thought fit to retain it 

 in the genus. Saville Kent suggests that it is in 

 reality the motile spore of some alga. 



Family Cercomonadidae, — "Animalcules naked, 

 free-swimming or adherent ; provided with a per- 

 manent or temporarily developed caudal filament ; 

 vibratile flagellum single, terminal; no distinct oral 

 aperture." 



Cercomonas crassicatida Stein. — The genus Cerco- 

 monas differs from Monas by possessing a posterior 

 prolongation made up of the same substance as 



Cercomonas, that is to say that it possesses a plastic 

 and changeable body, which is prolonged posteriorly 

 into a threadlike filament, and anteriorly bears a 

 single flagellum. It differs from Cercomonas in the 

 fact that it spends most of its time in a sedentary 

 condition, and it is solely with a view to this 

 condition that the tail is developed. This structure 

 is apparently merely a temporary elongation of 

 the body by which the animal clings to weeds or 

 decaying animal or vegetable matter. During this, 

 the sedentary period of existence, the flagellum 

 is used to sweep food particles within easy reach. 

 0. stcinii is regularly pear-shaped when situated 

 as before described ; but in nomad condition it 

 is quite irregular, being sometimes spheroidal, 

 sometimes ovate, or even elongate. The flagellum 

 undulates throughout, and is equal to the body in 

 length. The contractile vesicle is single and sub- 

 central, and placed just in front of the nucleus. 

 The length is 16 microns. 



