REPORT ON THE RADIOLARIA. ix 



the endoplasm, and the former is more vohiminous than the latter. 2. In all Eadiolaria the 

 division of labour is so . carried out between the central capsule and the extracapsulum, that the 

 physiological significance and independence of both principal parts of the cell is almost equally 

 great. 3. It is only in the Acanthakia that the formation of the skeleton takes place within the 

 central capsule; in all the other three legions it is quite independent of it. 



16. Tlie Malacoma and Skeleton. — Whilst the division of the unicellular organism 

 into central capsule and extracapsulum is undoubtedly the most important character of 

 the Eadiolarian organism, the development of a skeleton of peculiar and most varied 

 form is of very striking significance. This skeleton is always a secondary product of the 

 cell, but is always anatomically so independent, and so clearly marked off from the soft 

 parts or malacoma, that it seems advisable to regard both separately in a general 

 morphological survey. The skeleton stands in a different relation to each of the two 

 principal constituents of the malacoma. Only in the Agantharia is it centrogenous and 

 developed from the central capsule outwards. In the other three legions the skeleton 

 never arises in the centre of the capsule ; in the Nassellarta and Ph^odaria it is 

 always extracapsular ; in the Spumellaria it is also outside the central capsule originally, 

 but afterwards becomes often surrounded by it, and finally lies in most cases partly 

 within and partly without the central capsule. The chemical basis of the skeleton in the 

 Acantharia is the curious acanthin (an organic substance allied to chitin), in the 

 Ph^odaria a silicate of carbon, and in the Nassellaria and Spumellaria silica. 



17. Ground- Forms of the Eadiolaria {Promor2ihology). — The ground-forms of the 

 the Eadiolaria exhibit a greater variety than those of any other class in the organic 

 world, greater indeed than is to be found in all the remaining groups together. For every 

 conceivable ground-form which can be defined in the system of promorphology is actually 

 present in the Eadiolaria ; their skeleton exhibits, as it were, in material existence, 

 certain geometrical ground-forms which are found in no other organisms. The cause of 

 this unexampled richness in difierent forms lies chiefly in the static relations of the 

 Eadiolaria, which swim freely in the sea, partly also in the peculiar plasticity of their 

 protoplasm and the material of their skeletons. 



Eegarding the general system of ground-forms compare my Generelle Morphologie (1866, Bd. i. 

 pp. 375—552 ; Bd. iv., Allgemeine Grundformenlehre). The ground-forms there proposed and 

 systematically defined have, however, found but little acceptance (chiefly, no doubt, owing to the 

 difficult and complicated nomenclature) ; but having now, twenty years after their publication, 

 anew carefully revised and critically studied them, I can find no sufficient reason for abandoning 

 the principles there adopted. On the contrary the study of the Challenger Kadiolaria during the 

 last ten years, with its incomparable wealth of forms, has only confirmed the accuracy of my system 

 of ground-forms. The customary treatment of these in zoological and botanical handbooks (such 

 as those of Claus and Sachs) is quite insufficient. 



(ZOOL. CHALL. EXP. PART XL. — 1886.) El h 



