REPORT ON THE RADIOLARIA. xlv 



the vacuoles or " albumen globules " of Thalassicola nucleata and other ThalassicoUida, 

 as well as in the central capsule of Ccelographis and some other Ph^odaria (PL 127, 

 figs. 4-7). All these large crystals are probably to be regarded as excretory products. 



75a. Tlie Intracapsida7' Concrements. — Concretions, either mineral or organic, of 

 varying form and constitution, are to be found in the endoplasm of Radiolaria belonging 

 to very different families. They are most abundant and multiform in Tlialassicolla 

 nucleata, being usually circular or elliptical discs, which are concentrically laminated and 

 highly refractive, resembling starch-grains. Among them twin forms may frequently be 

 observed, as though the concrements were in process of division (see note A). Similar 

 amyloid concretions are to be seen in the central capsule of ditlerent Spumellaria and 

 Nassellaria, e.g., in Cephalospyris triangulata (PI. 96, fig. 28). Violin-shaped, highly 

 refractive concrements have been observed in the central capsule of numerous Spumel- 

 laria, Nassellaria, and Acantharia, e.g., Thala.ssosph(Bra, Spongosphcera, Plegmo- 

 sphmxi, Cyrtocalpis, Peripyramis, Botryocella, &c. (see note B). The chemical consti- 

 tution of these concrements is insufficiently known. 



A. The amyloid concretions of Tlialassicolla nucleata have been described in detail in my Mono- 

 graph (pp. 80, 250, Taf. iii. figs. 2, 3), and by E. Hertwig in the Histologie der Eadiolarien (1876, 

 p. 47, Taf. iii. figs. 9-13). 



B. The violin-shaped concretions of Thalassosphcera lifurca have been figured in my Monograph 

 (pp. 80, 261, Taf. xii. fig. 1). 



7&. The Intracapsulai' XantheUce. — The xanthellse, zooxanthellse, or symbiotic 

 " yellow cells " are found within the central capsule only in the Acantharia, whilst in 

 other Radiolaria they only occur in the extracapsulum. They are most frequent in the 

 Acanthometra, rarer in the Acanthophracta, but even in the former they are 

 often wanting. Their number is very variable, but usually small, from ten to thirty in 

 one capsule. They lie for the most part immediately below the capsule membrane, in 

 the cortical layer of the endoplasm. The form of the yellow cells is either spherical or 

 ellipsoidal, often also spheroidal or even lentiform. The diameter varies from O'Ol to 

 0-03 mm. They possess a distinct membrane and an excentric nucleus, and contain 

 numerous yellow pigment-granules in the endoplasm. This yellow pigment dissolves in 

 mineral acids to form a green fluid, and in other respects also behaves somewhat differ- 

 ently from the yellow pigment in the extracapsular yellow cells of the Spumellaria and 

 Nassellaria. In both cases, however, the xanthellse are not integral portions of the 

 organism, but unicellular alg£e, living as parasites or symbiontes in the body. 



A. The yellow cells in the central capsule of the Acanthaeia were first observed by Joh. Miiller 

 (L. N. 12, pp. 14, 47). In my Monograph I described them at greater length, and indicated their 

 differences from the extracapsular yellow cells of other Radiolaria (L. K 16, pj). 77, 86). Since then, 

 E. Hertwig has demonstrated their ceUtilar nature (L. N. 33, pp. 12, 113), and still more recently 



