344 



NATURAL HISTORY. 



Podocyrtis* (Fig. 10) lias a fenestrated, casque-like skeleton, globular where largest, then 

 tapering, and then spiked, at one end ; and open, with three marginal prickles, at the other. 



Eucyrtidium\ (Fig. 11) is a Polycistine, with a nearly conical reticulate skeleton, somewhat 



like a high-peaked Indian helmet of 

 chain-mail. 



Eucecryplialus^ (Fig. 12) has a 

 beautiful umbrella-shaped lattice as 

 a protection to its soft vesicular 

 body. 



The Poli/cistina are enveloped in 

 a delicate filmy investment of sar- 

 code, when alive ; and their sarco- 

 blasts or ovules are abundant. How- 

 ever complex the skeleton may seem 

 to be in any of these Radiolarian 

 forms, we must recollect that it is a 

 feature of less essential value in 

 biological classification than the in- 

 ternal organs. Therefore the Poly- 

 cistina are low in the scale (just 

 below the nucleated Radiolarians) ; 

 and, unless a " nucleus " should be 

 decidedly found in the Foraminifera, 

 these latter come last of all, among 

 the interesting and great family of 

 Rhizopoda. 



XLIV. In the last-mentioned 

 group we find the pseudopodia branch- 



Fig. 8. XIPHACANTHA MURRAYANA. (After W. Thomson.) 

 The skeleton of a Radiularian of the Acanthomctra type. Magnified 100 times 



another, and thus forming a mesh-work or i-eticulation. 



ing out and blending one with 

 Hence the Foraminifera have been 



placed among the Reticularia,\\ whenever the pseudopods have been taken for chief guidance 

 in grouping the forms. Some of 



* \ i 



10 



\ \ \ n / / 



9 



the Polycistina have a tendency to 

 this habit. 



One kind of Reticulose Rhizo- 

 pods (Lieberkiihnia) has neither 

 nucleus nor contractile vesicle, and 

 is therefore very low in the scale of 

 being ; others (Biomyxa and Gromia) 

 have both these endoplasts, or proto- 

 plasmic organs, and therefore rank as 

 high as the Amcebans. As to their 

 habits, some genera have representa- 

 tives in both fresh and salt water 

 {Gromia and Lieberkuhnia), some 

 only in fresh water (Biomyxa), some 

 only in salt and brackish water (Fo- 

 raminifera). 



The Reticularia, or Reticulose Rhizopods, protrude many long thread-like pseudopods, which 



* Greek, pous, a foot ; cyrte, a fish-basket. t Greek, eu, good ; cyrte. I Greek, cu, good ; cecryphalos, a hair-net. 



Latin, foramen (foraminis), a hole ; fero, I bear. This name was given to them originally, not on account of the 

 superficial perforations, but because their dividing walls have one or more simple holes ; and these were thought to constitute 

 a distinction from the tubed apertures in the divisions of the cephalopodous shells with which they were then confounded. 



II Latin, reticulum, a little net or a network. 



FigS. 9, 10, 11. RADIOLARIAN SKELETONS, OR LATTICED SILICIOUS 



SHELLS. Highly magnified. (After HaecTcel.) 



Fig.9,Sti/lodictya mittti.ipina. (fJaeckefi, living off Messina: Fig. 10, Podoci/rtis schombitrgii 

 (Ehreitberg), fossil from Barbadoes; Fig. 11, Eucyrtidium l&geua (Htiecket), living off 



