RECENT MEMOIRS ON FRESHWATER RHIZOPODA. 291 



Hertwig and Lesser regard the first two as absolutely 

 essential, rightly dismissing the so-called Coscinosphsera, 

 Stuart^ (referred by him to Radiolaria, but described as 

 having no central capsule) , as without doubt a Foraminifer, 

 the authors come to the second question as above. This 

 they at once answer for themselves in the negative, and 

 prefer to denominate the so-called freshwater " Radiolaria " 

 after Hackelas '' Heliozoa." They then proceed to discuss 

 the questions : 



1. Are the Heliozoa unicellular or multicellular or- 

 ganisms ? 



This is a question as regards the freshwater forms not 

 hitherto definitely taken up by any previous observers. It 

 is true that Greefi", speaking of Acanthocystis, alludes to 

 " vesicles containing a nucleus-like structure, and then offer- 

 ing the most complete resemblance to cells,"" and further on 

 alludes to " manifest cell-like structures," but without ex- 

 pressing any view as to the relation of these to the build-up 

 of this organism, or whether the observation has any wider 

 applicability, except as regards Actinos2)h(sriwn Eichhornii 

 ) where truly many nuclei coexist). 



Hertwig and Lesser, however, are of opinion that with a 

 few exceptions the Heliozoan individuals possess but the 

 value of a single cell. They regard, in fact, the median 

 globiilar (or ellipsoidal) body to be found therein as a 

 nucleus with its nucleolus — the whole surrounded by a mem- 

 brane (" Kernmembran ") — its appearance and structure 

 perfectly agreeing with the undoubted nucleus in Mono- 

 thalamia and other Rhizopoda. 



In this I believe they are perfectly right, and whilst in 

 my own published remarks I have hitherto rather leant to 

 the view of this central body being probably homologous 

 with the " central capsule" of the Radiolaria proper than 

 to be considered as a nucleus, it was still with hesitation — 

 with a " so-called " before either designation. 



An exception to the possession of but a single nucleus in 

 the Heliozoa is formed by Actinosph(eriu?7i Eichhornii. In 

 it, as is well known, are imbedded numerous nuclei, without, 

 however, any definite protoplasm territory being limited off 

 around each. Whether there be expressed hereby a true 

 " multicellularity" or not the authors naturally leave in 

 doubt, and would rightly restrict that term to such forms as, 

 with a multiplicity of nuclei, show an individualisation of 

 independent portions of the protoplasm no longer in con- 



1 Stuart, 'Zeits. f. wiss. Zool.,' Bd. xxvi, p. 328. 

 » Greeff, 'Arcbiv f. Mikr. Auat.,' Bd. v, p. 480, 



