168 PROr. ST. GEOUGE MIVAKT ON 



colony breaking up into spores of one kind only, those with crys- 

 tals. It is, however, possible that these two processes may indi- 

 cate two different species which resemble each other greatly, save 

 as to this reproductive process. 



Beyond the above described stages, no observations have as yet 

 gone, so that the mode of transition from the zoospore to the 

 capsule stage remains unknown. However, the zoospores have 

 no enveloping membrane, and the young central capsules are m 

 like case. If the latter (capsules) proceed directly from the 

 former, the Badiolaria so far resemble the Heliozoa ; and if the 

 processes observed by Miiller as existing in the young enclosed 

 AcanthometroB resembled the processes of such organisms as Acti- 

 nosplicerium, we have yet another approximation between these 

 two groups of Protozoa. 



Modes of Growfk. 



As to the modes of growth of the Radiolaria, Miiller pointed 

 out its three main modes : — (1) the unipolar, (2) the bilateral, 

 (3) the multipolar. 



The capsule does not change its shape, but when formed is at 

 once spheroidal, conical, or what not, with or without processes 

 or subdivisions. Thenceforth it only increases in volume. 



As to the skeleton, in addition to the three modes of growth 

 above noticed, there must be added that sudden mode of forma- 

 tion, that rapid deposition which seems to take place in the shell 

 of Collosphcera (as evidenced by its deposition round capsules in 

 the act of fission) and in the single or in the innermost spheroidal 

 shells of such forms as JEthmosphcera , CyrtidosphcEra, Heliospliaera, 

 SiplionospJicera, DiplospJicera, ArachnosphcBra, Rhapliidococcus, Gla- 

 dococcus, Coelodendrum, Haliomona, Ileliodiscus, Tetrapyle, Acti- 

 owmona, Didymocyrtis, RhizosphcEra, Spongosphcera, Dictyoplegma, 

 Spang odictyuon. 



Increase, even in the thickness of the network of the shell when 

 once formed, does not seem to take place ; for Haeckel found the 

 bars of Heliospli(sra inermis, S. tenuissima, and S. actinota con- 

 stantly the same in size in different individuals of the same species. 



Mtdtipolar growth takes place in the Acanthometrine forms 

 Splicer ozoum, Stylodicta, Lithelius, Actinomma, &c., and also in 

 the species of spine-bearing Polycystine forms and in the twigs 

 of Cladococcus. In these the skeletal parts go on increasing at 

 their apices, or (as in Sphcerozoum and most Acanthometrine 

 forms) all round also. 



