128 



THE RADIOLARIA 



of the scattered granules and vesicles about so many nucleated centres 

 in the endoplasm, and therefore as integral parts of the Radiolarian, 

 acting the part of storing reserve material. Brandt has shown that 

 their structure, though not suggesting this view of their origin, serves 

 to explain the connection between the pigment granules, pigmented 

 granular heaps, and definite yellow cells. Starting from the last, 

 with its single nucleus, plates of diatomih, numerous amyloid vesicles 

 and refractive granules, Brandt finds other xanthellae with multiple 

 minute nuclei, and by fragmentation of these yellow cells he accounts 

 for the presence of the isolated yellow granules, each of which, he 

 affirms, is a living corpuscle and possesses a very small nucleus 

 (10a, p. 237). This degeneration of the zooxanthellar nucleus into a 

 heap of chromatin granules, associated with the breaking up of the 



B. 



Fio. 17. 



A-C, yellow cells (zooxanthellae) of Aoantharia. (After Brandt.) A, large amoeboid cell 

 from Acanthonia tetracopa. B, C, spindle-shaped zooxanthellae (-4. tetracopa). D, single xan- 

 thella of Thalassophysa sangvinolenta, to show its cell-wall (C.w), hollow, singly refractive 

 inclusions that stain bluish violet with iodine. G, doubly refractive granules unaffected by 

 iodine, x 1000. 



cell, is probably not to be explained through digestion of the yellow 

 cells by the Acantharian, but as a consequence of the intimate 

 association between the two structures. Unlike the zooxanthellae of 

 the Spumellaria, which live, divide, and sporulate after the death 

 and dissemination of their host, those of the Acantharia lose their 

 power of independent existence, and when the endoplasm in which 

 they occur becomes transformed into isospores or heterospores they 

 too pass into these spores in the form of granules and starch 

 grains. Thus the flagellated heterospores of Xiphacantha alata 

 (Fig. 26, A) contain a mass of yellow granules, besides an amyloid 

 body (staining blue with iodine), which is constantly present in the 

 iso- and heterospores of this species. It is therefore possible that 

 the yellow cells of Acantharia pass from mother to offspring, and it is 

 certain that amyloid deposits are so transmitted. The zooxanthellae 

 of Acantharia, therefore, once they have entered the Radiolarian, 



