Ii6 THE RAD1OLARIA 



is inclined to consider the cone as due to the coalescence of axopodia 

 somewhat like those of the Acantharia (9, p. 439). 



The central capsule of the Phaeodaria possesses well-marked 

 characteristics in its double nature and the presence and structure 

 of its main opening or astropyle and of its two lateral parapyles. 

 The former consists of a teat-like operculum apparently striated on 

 the inner side owing to the septate character of the subjacent 

 eridoplasm. The latter are made up of an inner bulb and an outer 

 cone which opens on a prominence. The endoplasm under the 

 bulb is also radially grouped, and in general it may be said, as 

 evidence of the interchange of plasma through the capsular pores, 

 that the endoplasm in their neighbourhood has a striated character. 



The morphological character of the central capsule is a moot 

 point. Most authors, following Hertwig, hold it to be comparable 

 to the shell-membrane of a Thecamoeba, which, however, Dreyer 

 considers is covered by ectoplasm on both sides. It is possible, on 

 the other hand, that the capsule is a basement membrane peculiar 

 to the Radiolaria, and is a consequence of the differentiation of 

 their cytoplasm in relation to pelagic life. Until its development 

 is studied the question cannot be satisfactorily answered. 



Cytoplasm. The cytoplasm of Radiolaria, though one and con- 

 tinuous, is separable anatomically and physiologically into intra- 

 capsular and extracapsular portions. 



Flotation and dispersal, nutrition and stimulation are offices 

 that devolve chiefly upon the ectoplasm ; storage and reproduction 

 upon the endoplasm. During the early and nutritive stage of life 

 the ectoplasm is predominantly active, during the reproductive 

 phase the endoplasm is solely operative. Continuity of structure 

 and community of function are expressed by an interchange of 

 protoplasmic and metaplastic granules through and beyond the 

 capsular wall. 



The ectoplasm consists of four chief layers from within out- 

 wards : an assimilative zone of dense protoplasm around the 

 capsule, a thick alveolar layer capable of secreting gelatinous and 

 fluid spheres, an enveloping membrane guarding the animal from 

 contact with its environment, and beyond this a fringe of radiating, 

 contractile pseudopodia. This great development is primarily 

 related to flotation. From Brandt's researches on the hydrostatic 

 function of Radiolaria it is clear that the calymmal gelatinous 

 spheres play the chief part of this office. These spheres he holds 

 are viscous secretions of the ectoplasm and absorb water from 

 without inwards. The specific gravity of the expressed fluid 

 is, however, such as to point to water saturated with carbonic acid,, 

 and as we pass from the inner to the outer zones of this alveolar 

 layer, the spheres are found to become more and more vacuolar, 

 until at the surface they are so tense as to collapse at a touch.. 



