RECENT RESEAKCnES ON THE RADIOLAUIA. 181 



uo vacuoles. In the Ileliozoa, on the other hand, the 

 much fewer separated reproductive parts have each two 

 flagella (as in most Bhizopods), several contractile va- 

 cuoles, and a nucleus with vacuoles and nucleoli. 



(4) Yellow cells present in almost all Radiolaina, absent in 



Ileliozoa. 



(5) The Radiolaria are entirely marine, while the yet known 

 Heliozoa are almost entirely freshwater. 



(6) The pseudopodia of E-adiolarians have no axis-fibre similar 

 to that so often found in the Ileliozoa. 



The similarity between these two groups in external form and 

 chemical composition is undeniable ; but, as Hertwig points out, 

 very many of the Eadiolaria depart widely from the spherical 

 form, while the similarity of chemical composition cannot be con- 

 sidered as a distinction of great weight, seeing that the simi- 

 larity is shared with many other lowly organisms of quite different 

 affinities. The distinction as to the medium inhabited is also 

 much w^eakened by the discovery of the salt-water Heliozoa, Fina- 

 cocystis ruhicunda and Actinolophus pedunculatus. 



Again, though the differences which exist between the repro- 

 ductive processes (above enumerated as No. 3) are very great, yet 

 we must recollect tliat there are also great differences in this 

 respect between different Heliozoa, while the reproductive pro- 

 cesses of so few RadiolariaDs have yet been examined, that it 

 would be rash to feel confident that no important divergen- 

 cies will be hereafter found to exist amongst them in this 

 respect. 



AVith respect to the capsule itself (which seems to form so very 

 marked a difference) the distinction would be weakened if it 

 should turn out that young Eadiolarians which have not yet 

 acquired a capsule, nevertheless show a differentiation of their 

 sarcode into an inner and an outer layer, like the medullary and 

 cortical parts of Heliozoa ; and this may be indicated by Cien- 

 kowski*. The distinction would not only be weakened, but 

 would break down if it should be shown that certain adult Eadio- 



* See Archiv fiir mikrosk. Anat. vol. vii. p. 374, and pi. xxix. fig. 1. lie 

 says as to the young condition without a capsule, " Die jungen Kapseln sind 

 nackt ohne Schale in eine strahlende Protoplasm aschicht eingebettet, von keiner 

 scharf eonturirten Hiille umgrenzt. In diesem Stadium theilen sie sich hiiufig 

 durch Abschnlirung in zwei Halften." 



