870 THE ANIMAL KINGDOM. 



Separation of the fused individuals usually ensues in a few hours. It is 

 doubtful whether the phenomena detailed have any connection with re- 

 production. Encystation with its consequences (infra] may ensue, how- 

 ever, in Actinosphaeria made to fuse artificially 1 . 



Binary fission has been observed in comparatively few Heliozoa, 

 Actinophrys, Actinosphaerium, Acanthocystis, Clathrulina^ and Hedriocystis. 

 If Actinosphaerium is disturbed during the process, the incompletely 

 separated individuals reunite. In Hedriocystis transverse fission has been 

 seen in a young and still shell-less individual. The two (or four) parts 

 into which the individual divides in Clathrulina, retract their pseudo- 

 podia if they are not retracted before fission occurs, and one or all then 

 quit the shell, become Actinophrys-\\\ze, and finally develope a new 

 peduncle and shell. The young Clathrulina frequently attaches itself to 

 the old shell. Fission in the same animal may also give rise to three or 

 four parts ; if to three the larger part remains in the shell, the two 

 smaller quit it, as do all the parts when four in number. But the escaped 

 portions become biflagellate (uniflagellate, Foulke) spores, with a single 

 nucleus and some posteriorly placed contractile vacuoles ; they eventually 

 attach themselves and develope pseudopodia, a peduncle, and shell. Actino- 

 sphaerium may be multiplied by artificial fission. Gemmation appears to 

 occur in Acanthocystis and Clathrulina. A. viridis has been seen with 

 a small uni-nucleate sphere, possessed of a contractile vacuole and one or 

 two chlorophyl bodies lying beneath an elevation of the shell. It escaped, 

 became uni- or bi-flagellate, and then Actinophrys-Vfez. (Korotneff). In 

 A. aculeata round or oval nucleated bodies were observed by Hertwig lying 

 in a depression of the parent's body. They escaped through the shell, 

 and in some instances developed two flagella. A rounded and nearly 

 detached segment of the shell containing a non-nucleated (?) sphere of 

 protoplasm was seen in one specimen. The sphere was resolved into six 

 portions, which were set free one by one and became Actinophrys-Vfoo* 

 The parent produced a second similar structure. Clathrulina is said to 

 become vacuolate, and to develope small knobs on the surface which are 

 detached, become Actinophrys-\\ke, form a peduncle and shell 2 . 



1 Leidy has described a Raphidiophrys socialis, the individuals of which are simply entangled 

 by their pseudopodia. Gruber has found in Actinophrys sol that fusion may occur (i) between 

 two small non-nucleated specimens, (2) between a non-nucleated individual and a nucleated, a 

 specimen of the latter absorbing three of the former, but repelling a fourth, and (3) between two 

 nucleated individuals, repulsion however often occurring. He concludes that the process indicates 

 an augmentation of substance, and not a reproductive phenomenon. The non-nucleated individuals 

 referred to are of unknown origin. They have pseudopodia, an ecto- and endo-sarc, non-contractile 

 vacuoles, and sometimes a contractile vacuole ; they move and feed. See lit. p. 873, infra. 



2 Biflagellate zoospores have been seen given off from a green Actinophrys sol ; they sometimes 

 contained a chlorophyl granule (Archer, Q. J. M. x. pp. 306-7 ; xvi. p. 300). Biflagellate spores 

 have been also observed in the same Heliozoon by R. Hertwig (J. Z. xi. p. 340). Greeff saw a 

 multitude of minute Amoebae creep out of a dead Actino sphaerium and change into flagellate 



