80 FRESH-WATER RHIZOPODS OF NORTH AMERICA. 



Under the ith inch objective power of the microscope, many appeared 

 to be transversely striated. Similar bodies are described by Prof. Greeff as 

 a constituent of the endosarc of Pelomyxa palustris, 



Dr. Wallich describes a conspicuous nucleus and an equally conspicu- 

 ous contractile vesicle as present in Amoeba villosa, having the same essential 

 characters and holding the same habitual position as in Amoeba proteus. 

 In the figures accompanying Dr. Wallich's memoir, the single large nucleus, 

 and the large contractile vesicle, or in its place several smaller ones, arc 

 among the most striking features of the creature. 



In Pelomyxa villosa, except in those specimens I have regarded as 

 young individuals, I have at no time been able to detect a single large 

 nucleus like that represented in Amoeba villosa, or such as exists in A. proteus. 

 I have, also, at no time observed a single large and conspicuous contractile 

 vesicle in the more characteristic forms of the animal; but in its place there 

 are usually from one to half a dozen small ones, commonly occupying a 

 position in the vicinity of the villous area of the body, or even partly 

 within this area when it is produced as a process. Frequently the small 

 contractile vesicles are more or less obscured from view by other surround- 

 ing elements. They commonly remain separate and independant of one 

 another, and while one appears and undergoes enlargement another collapses 

 and disappears. 



I have not been able to trace a continuation of the history of Pelomyxa 

 villosa. 



In one instance I observed a large individual replete with quartz-sand, 

 apparently burst and scatter its softer granular constituents until reduced 

 to about one-half the original size. The remaining portion of the body 

 appeared unhurt, but what the phenomenon meant I did not positively 

 ascertain, though I suspected that it was attendant upon the expulsion of 

 germs. 



DINAMCEBA. 



Greek, deinos, terrible; amoeba. 



Animal with the same essential structure of Amoeba ; when at rest, 

 spheroidal or oval ; when in motion, habitually ovoid or slug-like, and with 

 the broader extremity in advance. Pseudopods few or many, mostly sim- 

 ple extensions of the ectosarc, subulate, or long conical and acute, occasion- 



