EEPORT ON THE RADIOLARIA. Ixxxix 



show a peculiar alveolar structure, numerous small compartments being enclosed between 

 two parallel plates. In the Circoporida (Pis. 114^117) and Tuscarorida (PI. 100) the 

 opaque porcellanous shell has a peculiar cement structure (§ 104), and the lattice- 

 structure is confined for the most part to characteristic rings of pores at the base of the 

 hollow tubes, which arise from the shell. The most peculiar lattice-work, however, 

 appears in the segmented shell of the Aulosphserida (Pis. 109-1 11) and Cannosphserida 

 (PI. 112). In the former the large meshes of the lattice-work are usually subregular 

 and triangular, in the latter polygonal ; the trabeculee are hollow cylinders, filled with 

 jelly, and containing usually a central axial thread. In each nodal point of the lattice, in 

 which three or more tangential tubes meet, these are separated by stellate or astral septa. 



135. Radial Spines of the Skeleton. — The skeleton in the great majority of Eadiolaria 

 is armed mth radial spines, which are of great importance in the development of their 

 general form and of their vital functions. From a morphological point of view the 

 number, arrangement, and disposition of the spines is usually the determining factor as 

 regards the general form of the skeleton. Physiologically they discharge distinct 

 functions, as organs of protection and sujjport ; they act also, like the tentacles of the 

 lower animals, as prehensile organs, since their points, lateral branches, barbed hooks, &c. 

 serve to hold fast nutritive materials. In general main-spines and accessory spines may 

 be distinguished in most Eadiolaria ; the former are of pre-eminent importance in 

 determining the figure of the skeleton ; the latter are merely appendicular organs. The 

 main-spines present such characteristic and important differences in the various legions 

 of Eadiolaria that they must be considered separately. 



136. Radial Spines of the Spumellaria. — The radial spines, which exhibit most 

 manifold variations in the large order Sphserellaria, present characteristic differences 

 in its four suborders. In the Spheeroidea their number and disposition serve for the 

 separation into families (p. 59); the Cubosphserida (Pis. 21-25) always possess six 

 radial main-spines, which stand opposite to each other in pairs and lie in three diameters 

 of the shell, which are at right angles to each other and correspond to the axes of the 

 regular crystallographic system. TJie Staurosphserida (PI. 15) have four spines, which 

 form a regular cross and stand opposite to each other in pairs, in two axes at right angles. 

 The Stylosphserida (Pis. 13-17) show only two main-spines, which are opposed to each 

 other in the vertical main axis of the body. Finally, the Astrospha^rida (Pis. 18-20, 

 26-30) are characterised by a larger and variable number of radial spines (eight, twelve, 

 twenty or more), sometimes regularly, sometimes irregularly arranged. Among the 

 other Sphajr ell aria thePrunoidea (Pis. 13-17, 39, 40) are most allied to the 

 Stylosphserida with two opposite main-spines ; the Discoidea (Pis. 31-47), on the 

 other hand, to the Staurosphserida with four crossed spines ; there exist, however, 

 Discoidea with two opposite, three marginal, or numerous radial main-spines ; it is 



(ZOOL. CHALL. KXP. PART XL. 1886.) Er VI 



