HELIOZOA. 869 



and Raphidiophrys. It is vesicular and has in the resting phase a distinct 

 nuclear membrane, a nucleolus and clear nuclear fluid. 



The pseudopodia are fine, straight, radiant, and developed from the 

 whole surface except in Actinolophus near the peduncle. They rarely 

 branch or anastomose. Their length varies from about one half the 

 diameter of the body, e.g. in Actinosphaerium to two or three times its 

 diameter, e. g. in Acanthocystis and Clathrulina. They can be displaced 

 from their radial position by currents of water, or bent at a sharp angle by 

 the sudden impact of a foreign body. They are supported by axial 

 filaments, which extend close to or up to the nucleus in Actinophrys ; 

 to just within the limits of the endosarc in Actinosphaerium, or to a 

 central corpuscle which unites them all, in Actinolophus , Acanthocystis, 

 Raphidiophrys, and perhaps Clathrulina 1 . In most cases they show a more 

 or less lively granule-stream. The movements of the Heliozoa, whether 

 on a solid surface or whilst floating suspended in water, are as a rule 

 extremely slow and as yet by no means explained. Some Heliozoa 

 appear to feed preferentially on animals, others on plants (algae, &c.), others 

 indifferently upon either. The pseudopodia draw the prey towards the 

 body, and in Actinosphaerium into a pit which closes over it. In Actino- 

 phrys a special broad pseudopodium-like process incloses the food, and the 

 same method is said to obtain sometimes in Actinosphae ium, Acanthocystis 

 and Raphidiophrys. There is generally a food vacuole. Faecal residues 

 are expelled anywhere, and have been seen extruded along a pseudo- 

 podium in Acanthocystis aculeata (Hertwig and Lesser). 



The species of Raphidiophrys and Sphaerastrum frequently occur in a 

 colonial condition. The skeletal envelopes of the individuals in a given 

 colony are fused. Each individual is united to its neighbours by slender 

 protoplasmic cords, and the pseudopodia radiating from the colony 

 come only from the outer surfaces of the individuals. Two or more 

 individuals of Actinophrys may become united by broad protoplasmic 

 bridges in which both vacuoles and food may be seen. These colonies 

 may change their shape, divide into sub-colonies, or their constituent 

 individuals separate. Partial or complete fusion between individuals of 

 Actinosphaerium has been observed, as well as between Actinosphaeria 

 produced by the fission of individuals artificially brought together. 



1 The axial filaments have been carefully investigated in Actinosphaerium by Brandt. They are 

 organic, not mineral, in composition. A new pseudopodium commences as a conical process ; a 

 needle-like structure within it is the first trace of its filament. A newly formed filament is readily 

 dissolved again by the protoplasm, an old one is more resistent : the former consists of vitellin (?), the 

 latter contains an admixture of other bodies. New filaments may fuse inter se, they may shorten by 

 contraction, and then either thicken, or display thickened nodes. The filaments, whether old or 

 young, are completely absorbed when the pseudopodia are retracted in encystation. It is pos- 

 sible that they may also be partially dissolved during an accidental contraction of the pseudo- 

 podia. 



