THE RADIOLARIA. 85 



may have the form of detached spicula, or of coarticulated 

 rods, or of networks, or of plates of silicious matter, often of 

 the most exquisite delicacy and beauty. Most of the Radi- 

 olaria are simple, solitary, and microscopical in size ; but 

 some, such as Collosphmra and Sphmrozoum (Figs. 5 and 6), 

 are formed of aggregates of such simple forms, and float, as 

 visible gelatinous masses, at the surface of the sea, which is 

 the habitation of the great majority of the JRadiolaria. 



The manner of multiplication and the development of the 

 JRadiolaria have not yet been thoroughly worked out. Cien- 

 kowsky, however, has observed, in Collosphmra, that the 

 protoplasm contained in the central capsule breaks up into 

 numerous rounded masses. The several capsules which are 

 associated together in the compound Radiolarian then be- 

 come isolated, by the dissolution of the protoplasm which 

 invested and connected them, and finally burst, giving exit 

 to the rounded bodies ; which, while yet within the capsules, 

 were observed to be in active motion. The germs (for such 

 they appear to be) thus set free are 0.008 mm. long, ovate, 

 and carry two flagelliform cilia at their narrow ends ; so that 

 they are " monads." Each has in its interior a crystalline rod 

 and a few minute oil-globules. The further development of 

 these mastigopods has not yet been traced ; but, if, as is 

 probable, they pass into young Radiolaria (which, according 

 to Haecke!, possess no capsule, but resemble Actinosphm- 

 ria), the Radiolaria, as members of the M^doplastica, would 

 typify Protomonas among the Monera. Neither conjugation 

 nor fission has been observed among the ordinary Radio- 

 laria, but both these processes take place in Actinosphm- 

 rium ; and, considering the resemblance of the young Radio- 

 laria to Actinosjyhmrium, it seems probable that conjugation 

 and fission will yet be discovered among them. 



Actinosplimriuyn has been observed to undergo multipli- 

 cation, by division of its central substance into a certain 

 number of spheroids, and every spheroid becomes inclosed in 

 a silicious case. After a period of rest, a young Actinosplim- 

 rium emerges from each of these cysts. 



The marine Radiolaria all inhabit the superficial stratum 

 of the sea, and must fabricate their skeletons at the expense 

 of the infinitesimally small proportion of silex which is dis- 

 solved in sea-water; but, when they die, these skeletons sink 

 to the bottom, and there accumulate, together with the Fora- 

 rninifera, in warm and temperate regions ; and with the 

 cases of the diatomaceous plants, which abound at the sur- 



