74 MICROSCOPICAL STUDIES. 



A higher division of the same Rhizopoda are the Foraminifera, 

 animals of the amoeba-type endowed with the faculty of building up 

 a skeleton, usually of lime (calcium carbonate), from whose surface 

 and from apertures in which, are given off numerous long whip-like 

 threads of protoplasm, or pseudopodia, locking and inter-locking with 

 one another (anastomosing) ; the same in kind, though differing mark- 

 edly in degree, as the few coarse and short pseudopodia of Amoeba. 

 Then we cross at once to the class we have to deal with, the Radio- 

 laria, where the power lies of building up a skeleton of flinty matter 

 (silica) the same in chemical composition as the fine quartz crystals 

 from which much optical glass is made. But this spicular coating is 

 not essential to existence, for many species (Collozoum) possess none. 

 Let me therefore consider such an individual, which may be taken as 

 representing the fundamental or primitive type of Radiolarian, the 

 skeleton being an after assumption in the class, though in Collozoum 

 the absence is not due to primitive want of it, but rather to dege- 

 neration. 



Comparing with Amoeba, we would Fay that in the Radiolaria 

 the body is usually of a globular form, and what answers to the 

 endosarc of the other, is separated from the outer layers by a 

 membrane (chitonous ?) which we term the capsular membrane. 

 This is pierced usually by numerous minute openings and bedded 

 in the protoplasm within the capsule (intra-capsular), lie several 

 nuclei a characteristic of the group, a very large oil-globule, and 

 a number of tiny crystals. 



The extra-capsular substance consists of two well defined layers, 

 the inner (sarcomatrix) which invests closely the capsule, is proto- 

 plasmic and granular ; while the outer layer, the calymna, is of a 

 structureless, gelatinous nature. From this layer arises an often 

 wonderfully beautiful flinty (siliceous) skeleton, built up sometimes 

 as a lattice-work bell, or it may be into a lace-work globe with great 

 projecting spines. The calymna is penetrated by delicate tubules 

 through which pass fine threads of protoplasm originating from the 

 sarcomatrix. Having passed through the calymna, these threads piss 

 out on the surface of the globe into a network, the sarcoplegma, and 

 from this are projected into the water around, long filamentous 

 pseudopodia, closely akin to those of the Foraminifera. With these 

 long tendrils, prey is entangled and is then passed inwards. 



The vast majority of Radiolarians and their name is legion 

 are such as we have described, but a small group live colonial lives, 

 numerous individuals massed in tiny communities, and modified in 

 certain points consequent upon the mutual duties devolving upon 

 the several individuals. 



