Protozoa. 27 



Near one end of the body there is usually a funnel- 

 shaped mouth opening into the inner protoplasm, 

 where digestion takes place, as in Rhizopods ; the un- 

 digested particles are ejected at a spot where the outer 

 wall seems deficient, and which sometimes is a distinct 

 opening. 



These animals multiply either by fission like most 

 of the other Protozoa, or else the nucleus breaks up 

 into egg-like masses which seem to develop into new 

 infusoria. This condition is preceded by the forma- 

 tion of a mucous mass around the animalcule, which 

 becomes quiescent, losing its cilia. 



The Vorticella, or bell animalcule (Fig. 13, c) is a 

 common form fixed by a slender footstalk, which on 



FIG. 15. FIG. 16. 



Noctiluca jniliaris, a marine luminous Acincta mystacina. 



animacule, showing its flagellum. 



irritation instantly contracts into a spring-like spiral 

 and the ciliary crown around the mouth of the bell 

 becomes introverted. Another common form, Ophry- 

 dium, has an outer gelatinous envelope, and as division 

 proceeds, this keeps the broods together so that they 



