RECENT MEMOIRS ON FRESHWATER RHIZOPODA. 297 



Here belong only the genera Actinophrys and Actino- 

 sphffirium. 



Actinophrys sol, Ehrenb. 



At any great length here to describe this^ one of the 

 longest known and most widely distributed of Heliozoa 

 (nay, Hertwig and Lesser take the marine form A. oculata, 

 Stein, for identical with that of the freshwater), would be out 

 of place^ at least unnecessary. Yet A. sol had been found 

 and recorded over and over again by observers everywhere 

 before the possession of a nucleus was suspected or noticed. 

 Even Hackel supposed it to be a moneron. The first to 

 detect it was Grenacher ;^ previously, indeed, the structure 

 was described in A. oculata, Stein,^ and confirmed by Carter.^ 

 It is perhaps curious that it should so long have escaped 

 observation, as in no freshwater Heliozoan is the nucleus 

 more easily perceptible. Of course, indeed, it is easy enough 

 to refind anything tvhen one knows it is there. It is some 

 years since I first noticed it, and had a sketch made of it as 

 regards a very large and fine but rather uncommon form of 

 A. sol, when I accidentally found that Grenacher had been in 

 advance of my discovery ; I then saw that it was present in 

 the ordinary, more minute, and more common form. Grenacher 

 was inclined to regard it, however (as at the time I was 

 rather of opinion myself), as " central capsule.'^ This struc- 

 ture possesses a globular figure, with a sharply-marked con- 

 tour and a smooth surface ; the contents appear to be of 

 palish-blue colour and finely dotted, though seemingly of 

 homogeneous consistence. Grenacher saw in this structure 

 seemingly but a hollow sphere containing a homogeneous 

 plasma, coagulating under acetic acid ; but as Hertwig and 

 Lesser regard it, this inner " coagulated " portion must be 

 taken as nucleolus. In the normal state the latter is not 

 readily seen. 



In some researches which I instituted on this nuclear 

 body I find that iodine and sulphuric acid produced little 

 effect as regards consistence of the nucleolus ; the outer wall 

 becomes more black and decided, the " contents " reddish. 

 Iodized solution of chloride of zinc rendered the nucleolus 

 plain, but best of all Beale^'s carmine fluid rendered it ap- 

 parent ; the nucleus became a lively red and the nucleolus 



' Grenacher, " Ueber Actinophri/s sol," in ' Verliandl. der Physic, med. 

 Gesellsch. zu Wurzburg,' Bd. 1 (1868), p. 170, t. III. 



' Stein, 'Die Infusionsthiere auf ihre Entwickeiungsgeschicbte unter. 

 sucht.,' p. 160. 



» Carter, • Ann. and Mag Nat. Hist.,' vol. v, p. 277. 



