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



Family VI. C o l l o s p h ^ E i d a, J. Miiller ^ (Pis. 5-8). 



Definition. — S p li se r o i cl e a living associated iu colonies, united by an alveolar 

 jelly-body, and connected by the network of anastomosing pseudopodia. 



The ffimily Collosphserida comprises all polyzous or social S p h se r o i d e a, 

 and constitutes the only polyzoic group among the Sph.'ERELLARIA. This group was 

 first constituted by J. Miiller as " Radiolaria j^olyzoa with shells." - Formerly 

 following his authority, in my Monograph I had separated them from the other 

 S p h se r i d e a and united them with the social Collodaria (Sphserozoida).^ Also 

 R. Hertwig in his Organismus der Radiolarien '^ united them with his Sphserozoea. In 

 my Prodi'omus ^ I had retained this isolated position. But a further careful study 

 has convinced me that this isolation is not truly natural, and that the CoUo- 

 sphserida are only " social Ethmosphajrida " which have arisen from this solitary sub- 

 family by adaptation to colonial life. There are some forms of CoUosphserida which 

 are nearly identical with some forms of Ethmosphserida, only differing from the latter 

 by their association in colonies ; and in some forms of both groups it is quite imj^ossible 

 to decide whether the isolated shells aj^pertain to one or to the other family. 



The isolated shell of the CoUosphserida is almost constantly (with few exceptions) 

 a simple extracapsular lattice-shell, as in the Monosphserida ; only the small group of 

 Clathrosphserida (with the genera Clathros][>]icBra and Xanthiosphoera) exhibit an 

 exception, the simple lattice-shell being overgrown by an external mantle or veil of 

 very thin, cobweb-like, irregular lattice-work (PI. 8, figs. 6—11). Therefore these 

 Clathrosphserida bear to the Acrosjahserida (or the common simple CoUospha^rida) a 

 relation similar to that which Liosphceva (p. 7G) bears to Cenosphcera ; both shells are 

 extracapsular " cortical shells " at a very short distance apart. In the CoUosphserida 

 true concentric meduUary shells never occur ; the central capsule always lies quite 

 freely in the simple or double cortical shell, separated from it by a jelly- veU. 



Although a well marked difference in the simple lattice-shell of the social CoUo- 

 sphserida and the solitary Ethmosphserida does not exist, nevertheless in most cases the 

 two shells can be distinguished by a practised observer. The simple fenestrated shells 

 of the monozoic Ethmosphserida are commonly quite regular spheres in a mathematical 

 sense, or regular " endospherical polyhedra " ; whereas in the CoUosphserida they 

 are commonly more or less irregular, often to an extraordinary degree (Pis. 5—8). 

 Some species of CoUosphserida, however, also possess quite regular spherical sheUs. 

 Another difference is often shown in the lattice-work of the shells, which in the 

 CoUosphserida is nearly always very irregular, and exhibits a peculiar tendency to the 



' Loc. CTi!.,pp. 17, 55, 1858. 2 Ahhandl. d. k. Akad. d. Wiss. Berlin, p. 55, 185M. 



' Loc. cit., p. 530, 1862. * Loc. cit., pp. 30, 133, 1879. 



' Loc. cit., p. 471, 1881. 



