180 PKOF. ST. GEORGE MIVAET OK 



The Relations of the Eadiolaria to other Organisms. 



That the Eadiolaria form a very well-defiued and distinct group 

 of Protozoa is admitted on all hands ; but the question at present 

 disputed is whether or not the resemblance between them and 

 the Heliozoa is such as to make it desirable to unite them as two 

 subdivisions of one larger group, itself distinct from all the other 

 larger groups of Protozoa. In his latest paper on the histology 

 of the Eadiolaria, Hertwig leaves the question undecided whether 

 it is the more natural arrangement to make, on the one hand, the 

 Heliozoa, Eadiolaria, and Thalamophora three distinct and co- 

 equal equivalent groups, or, on the other hand, to form two great 

 groups — the one containing the Heliozoa and Eadiolaria, the 

 other containing the marine and freshwater Thalamophora. 



On the whole, I am at present inclined to regard the Eadiolaria 

 as an altogether distinct group, and not to unite it with the 

 Heliozoa ; and at the same time it seems to me to be unquestion- 

 able that of all the above Protozoa, the Heliozoa are those which 

 come nearest to the Eadiolaria. 



In an earlier paper* he denied that any near relationship 

 existed between the Heliozoa and Eadiolaria. He made this 

 denial on the ground of the supposed cellular nature both of 

 the external and internal alveoli, and also of the " wasserhellen 

 BTdschen " as well as on other accounts. As he has now, how- 

 ever, become convinced that alveoli are but vacuoles without 

 membranous walls, and that the " wasserhellen BVdschen " are but 

 nuclei, these two reasons fall to the ground. The following 

 distinctions, however, seem still to remain intact : — 



(1) A porous capsular membrane present in the Badiolaria, 



absent in the Heliozoa. 



(2) A gelatinous investment present in the Radiolaria, absent 

 in the Heliozoa. 



(3) Eeproduction in the Radiolaria by means of numerous 



zoospores f, each with a nucleus and flagellum, but with 



* See Hertwig and Lesser, " Ueber Rliizopoden und denselben naheste- 

 hende Organismen," Archiv fiir mikrosk. Anat. yoL x. Suppl.-Heft, p. 147. 



t Such parts have not yet been found in any other Ehizopods, least of all in 

 the Heliozoa, in which a single procees of division gives rise to a small number 

 of individuals. The zoospores of Eadiolaria are most nearly resembled by 

 those of Myxomycetes ; but there the reproductive process is very different. 



