PROTOZOA. 39 



SARCODINA. HELIOZOA. 



One of the most familiar examples of the Heliozoa is 

 Actinophrys sol Ehr. (PL 43, figs. 1-3). Fig. i is the 

 young stage observed by Kent, which possessed a flagel- 

 lum. While swimming it projects blunt pseudopodia 

 from all sides (fig. 2). Its motions then become slower, 

 the flagellum is withdrawn, when suddenly thread-like 

 organs are put out in every direction and the animal is 

 transformed into the adult Actinophrys (fig. 3). If the 

 naked spherical body of a typical Rhizopod should re- 

 main constant in form, and the pseudopodia should radi- 

 ate as long thread-like organs and preserve this character 

 essentially unchanged, then we should have the Actino- 

 phrys in outward appearance. In the Heliozoa there 

 may be one or many nuclei. In Actinosphaerium, a 

 Heliozoan closely related to Actinophrys, from one to two 

 hundred nuclei are not uncommon, and this large number 

 in the adult is reached from one nucleus or a few nuclei 

 in the young (Biitschli). Actinophrys increases by fission, 

 and this sometimes gives rise to a colony. 1 



PI. 43, fig. 4, represents a young embryo of Clathrulina 

 elegans Cienkowski 2 which soon develops into the form 

 represented by fig. 5. Its striking resemblance at this 

 stage to Actinophrys is at once apparent. Like that 

 Heliozoan it is without a stem or a skeleton. In fig. 6 

 these have been developed, the stem being secreted first, 

 but both are as yet nearly colorless. Fig. 7 is the sta- 

 tionary adult with its stem (only part of which is shown 

 in the drawing) and skeleton. The pseudopodia extend 

 in all directions from the openings of the shell. After a 

 time these are drawn in and fission takes place, each prod- 



1 For views in regard to the process of conjugation of Actino- 

 phrys and the Heliozoa in general, see Btitschli, Bronn's Thier- 

 Reich, I, 1881, p. 317. 



2 See Arch. f. mikr. Anat., Ill, 1867, p. 311. 



