3a 



ZOOLOGY. 



tion is then carried on by tlie help of the lip alone, which 



expands latterly until it 

 completely overlies the 

 particle. All this is done 

 quite rapidly, in a few sec- 

 onds, and then the food 

 glides quickly into the 

 depths of the body, and is 

 enveloped in a digestive 



Fig.20.-Moiiaas(Di;««a).-AfterTatUe. ^ac^ole, whilst the Up as- 



gumes its usual conical shape and proportions. " (Clark.) 

 All the monads have a contractile vesicle. In Monas- 

 termo, Clark observes that it is " so large 

 and conspicuous that its globular form 

 may be readily seen, even through the 

 greatest diameter of the body ; and con- 

 tracts so vigorously and abruptly, at the 

 rate of sis times a minute, that there 

 seems to be a quite sensible shock over 

 that side of the body in which it is em- 

 bedded." The contractile vesicle is 

 thought to represent the heart of the 

 higher animals. The reproductive organ 

 may possibly be represented in Monas 

 termo by a "very conspicuous, bright, 

 highly refracting, colorless oil-like globule 

 which is enclosed in a clear vesicle" called 

 the nucleus. This and other monads live 

 either free or attached by a slender stalk. 

 As an example of the compound or aggre- 

 gated monads may be cited UceUa, prob- 

 ably glauconia of Ehrenberg. Otlier 

 forms, as Codosiga, are fixed by a stalk to 



some object (Fig. 21, C. pulclierrimna „. 



ni 1 \ r i.1,- 1 11- J J. .1 , n Fie. 21.-.-t. Corfo-wm 



Oiarkj. in this and allied forms the body pw'cAejTjmi/s. d. the- 

 is surmounted by a collar or calyx out of ^"Issfra^'twl '2e"° fl,I- 

 which the flagellum projects. The Co- a/L'p^S^fiu^vJr- 

 dosiga has been observed by Clark to un- '^•--"'« ciurk. 

 dergo fission, two independent monads resulting, within th& 

 space of forty minutes. 



