RECENT EESEARCHES ON THE RA.DIOLARIA. 143 



are soluble both in acids and alkalies. It may be that they are 

 undigested remnants of food. 



Other bodies *, of a crystalline structure, are found in a very 

 few forms, such as Collozoum, Splicerozoum, Thalassieolla, and Gol- 

 losplicera. Those in the last-named genus are about -^~" long. 

 These crystals are said to be insoluble not only in cold and hot 

 water, but even in cold or hot acids and alkalies. 



In a single Eadiolarian {Physematiwn 3£ulleri) Haeckel found 

 scattered round the inside of its capsule groups of three to five 

 pear-shaped cells 0"05-006 millim. iu length, with their apices 

 mediadf, each enclosed in a membrane and with a granular nu- 

 cleus. The broad end of each group lies against the inner sur- 

 face of the capsule. Haeckel suspects that it may be perforated, 

 and so serve as a channel of communication between the intra- 

 and extracapsular sareode. He calls these groups of cells " cen- 

 tripetal Zellgruppenr 



As before said, the extracapsular sareode invests the capsule 

 more or less thickly on all sides, and is itself invested exter- 

 nally by a more or less perceptible gelatinous layer; but no 

 membrane exists beneath or outside that layer. 



Alveoli are present in this part of the sareode of a few 

 simple Eadiolaria {Thalassieolla, Aulacantha) and in all the com- 

 pound forms, where their great number and size seem the main 

 conditions of the volume of each colony. One excessively large 

 nucleus may occupy the centre of the colonj^, as in GollosphcBra, 

 showing one large central alveolus, with circumferential fully- 

 developed capsules and other more central capsules in process of 

 development, also many yellow cells amongst the radiating pseu- 

 dopodia and the circumferential capsules. The alveoli may, on 

 the contrary, be much larger superficially and smaller within, as 

 in Thalassieolla ; they are, of course, bounded on all sides by the 

 sareode, and in the complex forms are bordered by those of the 

 pseudopodia, which radiate inwardly from the several zooids. 



The extracapsular sareode also sometimes contains pigment 

 which is generally black, or black -brown, or red-brown, or dark 

 violet. It is aggregated in granules or vesicles, and is generally 

 collected towards the deepest layer next the capsule. 



Nothing at all resembling concretions is found in the external 



* See Miiller, Abhandl. Berlin, 1858, pi. viii. fig. 9 ; and Haeckel, I, c. pi. iii. 

 fig. 3. 



t ' Radiolarien,' pi. iii. fig. 7 ; and Kolliker's ' Icones Histologictp,' pi. iv. 

 fiK-7. 



