REPORT ON THE RADIOLARIA. XXIX 



species indeed only just prior to the development of the swarm spores. I have recognised the 

 presence of it in all species which I have investigated (more than a thousand), and even in those 

 in which Brandt denies its existence. It is often very delicate and may easily be overlooked, 

 especially when the contents of the capsule are colourless, but in all cases by the prudent 

 application of staining fluids and other reagents its presence may be demonstrated. Even in those 

 cases in which the contour of the capsule was not visible, and its contents appeared to pass 

 without definite boundary into the matrix of the extracapsulum, it was possible by the use of 

 appropriate stains or reagents, which would not penetrate the capsule, or of those solvents which were 

 capable of dissolving its contents and of causing it to swell up like a distended bladder, to recognise 

 the existence of the membrane. Those Radiolaria in which it is truly absent are young animals of 

 species in which the membrane is only formed immediately before sporification, and persists but 

 for a short time (e.g., species of Collozoum, Sphcerozoum, Acanthometra, Acanthochiasma, &c.). 



57. The, Capsule-Openings of the Peripylea (or Spumellaria). The capsule-membrane 

 of the PERIPYLEA is generally perforated by extremely fine and numerous pores, which are 

 distributed at equal distances over the whole surface, and are precisely alike in all parts 

 of the capsule. Hence the SPUMELLARIA may be called " Holotrypasta " or "Porulosa"; 

 they agree with the ACTIPYLEA in being devoid of an osculum or operculum ; they are 

 distinguished from the latter group mainly in that their pores are equally distributed 

 over the whole surface of the capsule, whilst in the ACTIPYLEA the pores are disposed in 

 definite groups or lines, separated by large imporous areas. 



The central capsule of the SPUMELLARIA, with its innumerable fine and evenly distributed pores, 

 must be regarded as the primitive arrangement, from which the different central capsules of the 

 three other legions have been developed. The central capsule of the ACTIPYLEA has been derived 

 from that of the PERIPYLEA by reduction in the number of the pores and their distribution in 

 definite, regularly disposed areas in the membrane. The central capsule of the Osculosa is 

 characterised by the formation of a special main-aperture (osculum) at the basal pole, which is 

 closed in the MONOPYLEA by the porochora, and in the CANNOPYLEA by the astropyle ; the 

 remaining pores, with the exception of the accessory openings of many CANNOPYLEA, remain un- 

 developed in both these legions. In the same way Hertwig regards the central capsule of the 

 PERIPYLEA as the primitive form (1879, L. N. 33, p. 107). 



58. The Capsule- Openings of the Actipylea (or Acantharia). The capsule-membrane 

 of the ACTIPYLEA is perforated by very numerous fine pores, which are regularly distri- 

 buted over the surface of the central capsule, and separated by imporous intervals. 

 Hence the ACANTHARIA belong to the "Holotrypasta" or "Porulosa"; they have 

 neither osculum nor operculum, and agree in this particular with the PERIPYLEA ; but 

 they are separated from these latter chiefly by the fact that their pores are much less 

 numerous, and marked off into regularly arranged groups or lines by imporous intervals. 

 In the PERIPYLEA, on the contrary, the pores are much more numerous and are evenly 

 distributed over the whole surface of the capsule. 



