RECENT MEMOIRS ON FRESHWATER RHIZOPODA. 303 



denominates these *' spherical bodies " within " reproductive 

 cells" — the former, no doubt, Schultze's nucleoli, the latter 

 the true nuclei. 



Corresponding to the large size of this species the pseudo- 

 podia are very large and long ; they are developed all over 

 the globular body ; as to the axile threads, as before men- 

 tioned, Hertwig and Lesser regard them as mere strengthen- 

 ing apparatus for the pseudopodia, and are opposed to 

 Greeff's view as regards their nature. Greeff would regard 

 them as skeleton-spines ; but true spines are rigid, withstand 

 the action of acids ; on the other hand, these slender linear 

 axes are flexible, and disappear under reagents. It is not 

 even clear that they may not be withdrawn Avith the pseudo- 

 podium and ve^tYodnced pari passu therewith. (See remarks 

 further on.) Again, in regard to the true spines of other 

 forms, the pseudopodia do not form a complete investment 

 around them, but they lie apart from the body in an external 

 stratum. 



It is, of course, needless to urge that Actinosphserium is a 

 true Heliozoan,not a Radiolarian. Its affinityj and, indeed, 

 resemblance to Actinophrys sol is considerable, and they have 

 often been confounded, as by Kolliker, and, indeed, Wallich 

 has sought to show they are not distinct ; but this is no more 

 than he has done in other instances equally untenably. In 

 the fully-grown Actinosphaerium, besides the great difference 

 of size, the nuclei are numerous, the two regions, both 

 alveolar, distinctly marked ; in Actinophrys, the nucleus is 

 single and the endosarc homogeneous, passing by degrees into 

 the vacuolar ectosarc. 



It is true that young forms of Actinosphaerium are no 

 larger than some examples of Actinophrys sol, but there is, 

 to my own eyes, always something about the youngest and 

 least developed specimens of the former that tells at once 

 which species it belongs to. As Hertwig and Lesser point out, 

 the alveolae of the former are always larger than in the latter ; 

 the pseudopodia of the young specimens of the former are 

 often very few and short, but are always numerous in the 

 latter. I must, for my part, wholly concur with Hertwig 

 and Lesser that the two forms are essentially specifically 

 distinct, and further that they ought to be maintained as 

 types of two distinct genera, in accordance with Stein and 

 Haeckel. 



Professor F. Eilhard Schulze records some valuable and 

 interesting observations on the structure, and subsequently 

 confirms previous observations on the development of Ac- 

 tinosphcerium Eichhornii, Stein = Actinophrys Eichhornii, 



