GENUS ACTINOPHRYS— ACTINOPHEYS SOL. 237 



slowl}- expanding and rising- above the surface of the body, looking like an 

 air-bubble floating on Mater. Reaching its full size as a sphere, half 

 imbedded in the foamy-looking structure of the body, on a sudden it col- 

 lapses, and a slight sinking occurs of that part of the body in which it 

 was situated. The collapse of the contractile vesicle and the discharge 

 of its contents impart a feeble tremor to the whole bod} T , and this tremor 

 may often be noticed, evidently from the same cause, even when the 

 contractile vesicle is out of sight. The reappearance of the contractile 

 vesicle commonly takes place in the same position that it previously occu- 

 pied. Gradually expanding, it rises as a film of granular protoplasm, 

 which, becoming thinner and thinner, finally bursts, and gives exit to the 

 liquid contents. 



The interior of the body of Actinophrys sol frequently exhibits, among 

 its clear vacuoles, a variable number of colored and colorless granular balls, 

 which are often included in liquid drops or vacuoles. These are food-balls, 

 and may be situated at various depths from the surface. The colored balls 

 are usually green, dependent on algae or zoospores used as food, or they 

 may appear brownish or reddish, due to changes produced by digestion. 



The pseudopods of 'Actinophrys sol are ordinarily very numerous, though 

 variable. They are delicate extensions or rays from the granular proto- 

 plasmic basis of the body, and are commonly so straight and fixed in 

 position as to resemble fine acicular crystals. They are, however, quite 

 flexible, so that when the animal is accidentally pressed against a resisting 

 body they will bend like the hairs of an artist's pencil. They are retractile, 

 though the animal ordinarily seems so little sensitive that they remain 

 projected, notwithstanding any disturbance. They range in length equal 

 to the diameter of the body, to two, three, or more times that extent. 



Grenadier, and Hertwig and Lesser, describe the pseudopodal rays as 

 being sustained by an axial thread of firmer consistence than the granular 

 protoplasm occupying the exterior. I have been unable to confirm the 

 statement of these authorities, and to me the pseudopodal rays seem to be 

 nothing more than the most delicate filaments of viscid granular protoplasm. 



Actinophrys sol ordinarily remains almost stationary in position sus- 

 pended in water, but closely watched it is observed to glide slowly through 

 its element without obvious cause, but probably as the result of some not 

 easily detected action of the numerous rays. 



