270 FRESH-WATER EHIZOPODS OF NORTH AMERICA. 



The supposed encysted forms consist of an outer sphere, bristling with 

 delicate, simple, spinous rays, but without pseudopodal rays. The sphere 

 is composed of a doubly contoured membrane, apparently cancellated, and 

 filled with a clear liquid, including a second sphere. The latter is invested 

 with a membrane like that of the outer sphere, but is devoid of spines, and 

 is occupied with colorless granular protoplasm mingled with abundance of 

 oil molecules, giving the contents a milky appearance. 



With the foregoing I have occasionally met with empty membranous 

 sacs, and fragments of others, as seen in fig. 13, which I have regarded 

 as the remains of the capsule of encysted forms of the same species of 

 Acanthocystis. 



ACANTHOCYSTIS — ? 



Plate XLIII, figs. 14-16. 



Body spherical, composed of a basis of colorless granular protoplasm, 

 with a central nucleus, and with variable proportions of bright-green and 

 colorless corpuscles or with colorless ones alone. Spinous rays numerous, 

 short, pin-like in form. 



Size.— From 0.039 mm. to 0.051 mm. 



Locality. — In water among floating alga?. Pennsylvania. 



A third kind of Acanthocystis, distinguishable from the two former by. 

 the shortness and pin-like character of its spinous rays, I have occasionally 

 seen, but under circumstances unfavorable to making a full investigation 

 of the animal. 



In August, in water with Spirogyra, collected from the fountain at the 

 entrance of Fairmount Park, Philadelphia, I observed a number of color- 

 less individuals of Acanthocystis apparently passing into the encysted state. 

 Seven specimens ranged from 0.039 mm. to 0.051 mm. in diameter. They 

 were without pseudopodal rays, and mostly were completely inactive. The 

 exterior of the body was mammillated and densely covered with short pin- 

 like spines about 0.006 mm. long. 



In one individual, represented in fig. 14, pi. XLIII, the body was a 

 mass of granular protoplasm, mingled with fine oil molecules and a few 

 larger ones, together with a nucleus and a clear vacuole nearly as large as 

 the latter. 



Another individual, represented in fig. 15, consisted of a membranous 



