RHIZOPODA. 



13 



Oedee III. — HELIOZOA. 



The Heliozoa, or sun-animalcules, are very beautiful Rhizopods, inhabiting fresh 

 water. Most of them are spherical, floating forms, but a few are attached by long 

 pedestals or stipes. The pseudopodia are in the form of delicate, tapering rays, extend- 

 ing outward in all directions from the centre, often exceeding the diameter of the body 

 in length. They are flexible, more or less contractile, and sometimes reveal a slow 

 circulation of granules along their 

 length. The sarcode is not distinctly 

 differentiated into endosaro and ec- 

 tosarc, but in one interesting form, 

 Actinosphcerium, the outer sarcode is 

 a frothy, vacuolated mass of consider- 

 able thickness. 



The most common of the Heliozoa 

 is the Actinosphrys sol. It is found in 

 pools of standing water almost every- 

 where, among the floating plants, ap- 

 pearing under a low-power of the 

 microscope as a colorless, spherical 

 body, varying in size from .04 mm. to 

 .12 mm. in diameter, with innumer- 

 able delicate, bristling spines three 

 or four times the diameter of the body 

 in length. The sarcode is full of vac- 

 uoles, which give it a frothy appear- 

 ance. Watching the minute sphere a 

 few moments, there will probably be 

 seen somewhere along the periphery a 

 slowly distending vesicle, which reaches 

 a certain size, and then suddenly col- 

 lapses. This is the contractile vesicle. 

 The first description of this curious, 

 little creature seems to have been given 

 by a French naturalist, who referred to 

 it, if we may translate the bad French 

 in which it is written, with some dis- 

 cretion — as "a fish, the most extra- 

 ordinary that one could see." 



The food of Actinophrys consists 

 of minute infusoria, diatoms, and other 



unicellular alga, which frequently can be seen within the body as green balls. The 

 pseudopodal rays are used as organs of locomotion, and for the prehension of food. If 

 an active infusorian comes in contact with the spines it seems to be paralyzed. If the 

 prey be very minute it will be seen to glide along the rays very gradually until it reaches 

 the body, when a portion of the sarcode is projected to envelop it, and draw it mto the 



Flo. 10. — Clathrulina elegans, enlarged 350 times. 



