REPORT ON THE RADIOLARIA. 1525 



majorit)' of the other Radiolaria ; in some gigantic forms tlic (liameter of tlie unicellular 

 body reaches 20 or even 30 mm. 



The Central Capsule of the Ph.eodaria is the most important part of their body and 

 preserves in all families of this legion the same essential structure, and nearly the same 

 form, in striking contrast to the extraordinary variety and complication of the skeleton. 

 As alread)^ mentioned, it differs from the central capsule of all the other Radiolaria 

 in two most important peculiarities ; firstly, the double membrane of the spheroidal 

 capsule, and secondly, the singular structure of its constant main-opening, the astropyle. 

 A third constant character is the considerable size of the enclosed nucleus, the diameter 

 of which usually equals about half of that of the capsule itself. 



The diameter of the capsule is, in the majority of Ph^odakia, O'l to 0"2 mm., often 

 also 0"3 to 0'4, rarely more than 0'5, or less than 0"05 mm. 



The position of the central capsule is somewhat different in the four orders into 

 which we have divided the Ph.eodaria. It lies in the centre of the spherical, concentric 

 calymma in all the P h se o c y s t i n a, or in those Ph^odaria which possess no complete 

 lattice-shell — Phasodinida, Cannorrhaphida, and Aulacanthida (Pis. 101-105). The 

 P h £6 s p h a3 r i a (comprising the Orosphserida, Sagosphaerida, Aulosphaerida, and 

 Cannosphserida, Pis. 106-112) all possess a very big, usually spherical lattice-shell, 

 and here the central capsule is much smaller than the latter and lies in its centre. 

 Another position is constantly occupied by the central capsule in all P h se o g r o m i a 

 (Pis. 99, 100, 113-120; the families Challengerida, Medusettida, Castanellida, 

 Circoporida, Tuscarorida), which have a peculiar mouth on the lattice-shell, placed on 

 the oral pole of its main axis ; the central capsule lies in the opposite aboral half of the 

 shell cavity. The Phajoconchia finally (Pis. 121-128, the families Concharida, 

 Coelodendrida, and Ccelographida) all possess a bivalved shell, and the capsule is here 

 enclosed between the two valves of the shell. 



The form of the central capsule is constantly spheroidal, slightly depressed in the 

 direction of the main axis, and therefore comparable to the spheroidal form of our globe. 

 The depression is generally very slight, so that the proportion of the minor vertical 

 main axis to the major horizontal or equatorial axis is about 4:5 or 5 : G, often even 

 8 : 9 or less ; but sometimes the proportion becomes 3 : 4, or even 2 : 3, so that the capsule 

 becomes nearly lenticular ; very rarely its form becomes almost perfectly spherical 

 (PL 101, fig. 1). The main axis stands always vertically, and is distinctly marked by 

 the peculiar shape of the astropyle, placed on its oral pole. Usually this pole, in the 

 living and freely floating Ph-^eodaria seems to be the lower pole, directed downwards 

 (as also in the Nassellaria) ; but in some families it seems to be inversely directed 

 upwards, as in the Challengerida and Tuscarorida (Pis. 99, 100). 



The two membranes of the central capsule possess in all PH^i:oDARiA a very different 

 shape, and were in all preparations which I could accurately examine (some hundreds 



