THE RADIOLARIA 99 



free during the decomposition of reserve materials, and so long as 

 the waste products evolved in this process are removed, respira- 

 tion will continue in a medium deprived of free oxygen. Such a 

 view enables us to consider the reserve materials of Radiolaria 

 as of respiratory as well as of nutritive significance. It is not 

 improbable that the respiration of the endoplasm (in which these 

 fatty and stratified reserves occur) is of a different character from 

 the more violent exchange which seems to occur in the ectoplasm. 



In connection with destructive metabolism we may summarise 

 our view on the nature of excretory processes in Thalassicolla. That 

 carbonic acid and nitrogenous excreta are formed in abundance 

 seems certain from the rapid destruction and regeneration of the 

 calymma and its vacuoles, but there is no accumulation of excretory 

 substances such as occur in most Rhizopods. It is suggested, en 

 the basis of experiments* with Turbellaria (Gamble and Keeble [41]), 

 that this absence of excretory matter is due to the activity of the 

 yellow cells, which are attracted to their host chemotactically and 

 from which, by the uric acid or urea therein, they derive their nitrogen. 

 In the same way such a view affords an explanation of the associa- 

 tion of zooxanthellae with Radiolaria, and of the apparently con- 

 comitant absence of excretory granules. Additional proof of the 

 correctness of this view lies in the fact that such granules occur 

 massively and constantly in one division of the Radiolaria (the 

 Phaeodaria or Tripylaria), and that in this division, and in this 

 only, zooxanthellae are as constantly absent. 



Reproduction. In addition to multiplication by simple fission 

 (25a), Thalassicolla has two true reproductive processes, which, how- 

 ever, never occur in the same individual. These processes con- 

 cern the formation of spores, which are of two kinds, isospores 

 and heterospores. A given Thalassicolla is, therefore, isosporous or 

 heterosporous. 



When the reproductive period ensues, the protoplasm and its 

 contents undergo a metamorphosis, which results in the transforma- 

 tion of the endoplasm into a mass of flagellated spores, in the dis- 

 integration of the calymma, and the separation of the sporulating 

 capsule from its envelope. The relatively heavy capsule descends 

 to a depth of 300-400 metres, its wall bursts, and its spores are 

 liberated. In the case of isospores these bodies are of uniform 

 shape and size (Fig. 2, D) ; in the case of heterospores (L, M) two 

 varieties occur, of which the larger are not only twice the size of 

 the smaller ones, but possess other distinctive characters which are 

 given below. 



The formation of isospores in Thalassicolla nucleata proceeds as 

 follows (Brandt [26]). The nucleus and endoplasm undergo a 

 series of changes. The chromatin, previously coiled up in a thick 

 thread, becomes evenly granular, and the micleoplasm acquires an 



