58 THE VOYAGE OF H.M.S. CHALLENGER. 



regular cube (PI. 18, lig.s. 1-3) ; (b) twelve spines (placed iu the corner axes of the 

 regular icosahedi'ou) ; (c) fourteen spines (six placed in the three dimensive axes of the 

 regular octahedron, eight in the centres of its eight faces); (d) twenty spines (placed either 

 iu the same order as in many L a r c o i d e a and Acantharia [?], or iu the twenty corners 

 of the regular dodecahedron) ; (e) thirty-two spines (twelve placed in the twelve corners 

 of the regular icosahedron, twenty in the centre of its triangular faces). Besides these 

 most important and quite geometrical modes of disposition there also seem to occur in 

 the Astrosphcerida the following subregular (or symmetrical?) modes : 9, 10, 16, 18, 24, 

 40, 60, 80. But it is very difficult to give a correct account of these modes. In 

 every case this manifold and regular disposition of the radial spines is of the highest 

 interest for the study of general " Promorphology." 



The Central Capsule is in all S j) h se r o i d e a (without any exception) a perfect 

 sphere in the geometrical sense, even in those forms in which the enclosing lattice-shell is 

 more or less irregular (i.e., many Collosphserida). This is the most important character, 

 which separates the S p h ae r o i d e a from all other S p h fe r e 1 1 a r i a. For in the 

 P r u n i d e a the capsule is ellijDsoidal, with one prolonged axis ; in the D i s c o i d e a 

 lenticular, with one shortened axis ; in the Larcoidea lentelliptical, with three 

 different dimensive axes. The central capsule is originally always enclosed by the 

 lattice-shell ; but in many cases with increasing growth this relation becomes inverted ; 

 the capsule sending out many club-shaped blind sacs through the meshes of the lattice- 

 shell, and these melting together outside the latter, a new membrane is formed, enclosing 

 a " medullary sheU." 



The Nucleus of the cell exhibits a very different shape in the solitary and the social 

 S p h aj r o i d e a. In the solitary or monozoic Sphajroidea the centre of the 

 central capsule is occupied by a large spherical concentric nucleus, with or without 

 nucleoli ; also this nucleus is originally always within the innermost lattice-shell, but 

 with increasing size may overgrow and enclose it. A short time before the formation 

 of the vibratile spores the central nucleus becomes resolved into many small nuclei. In 

 the social or polyzoic S p h se r o i d e a — the Collospha^rida — commonly the simple central 

 nucleus very early (a long time before the formation of the spores) is divided into a 

 great number of small nuclei, whilst the centre of the capsule becomes filled with a 

 large oil-globule. Therefore we find the same difference between the solitary and 

 social forms in the S p h se r o i d e a as in the C o 1 1 o i d e a. Here also the calymma, 

 or the jellj^-mantle, enveloping the central capsule, is in the social forms very large and 

 voluminous, differentiated into alveoles, whilst in the solitary forms it is much smaller, 

 without alveoles. 



