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



the capsule (the central star of the skeletou). These radial pyramids are, however, but 

 rarely visible, being usually more or less concealed by a dark j^igment. 



The differentiations of the endoplasm in the central capsule of the Actipylea have been but 

 little investigated, but they appear to vary somewhat in the different groups of this legion. In all 

 AcANTHAEiA in which the twenty radial bars are regularly arranged according to the Mtillerian law 

 (see p. 7l7) and in which axial threads constant in number and disposition run between tbem from 

 the central star to the capsule-membrane, it obviously follows that the endoplasm must be divided 

 into more or less distinct radial pyramids, and this must be the case whether these take the form of 

 continuous tracts or of actually separable portions. The regidar polygonal figures, often seen on the 

 surface of the central capsule (with special distinctness in AcantJwmctron elasticum and Acantlio- 

 metron pellucidum) separated by a network of granular threads, are the bases of such radial 

 pyramids (see Hertwig, L. N. 43, p. 12, Taf. i. figs. 1-7). 



79. The Endoplasm of the Monopylea. — The intracapsular protoplasm of the 

 Nassellaria or Monopylea is distinguished from that of any of the other three legions 

 by the development of a quite peculiar fibrillar structure, the axial " pseudopodial cone," 

 which may shortly be termed the " podoconus " (foot-cone). Since this is in direct 

 correlation with the peculiar structure of the capsular opening, the large " porochora," 

 which is situated at the basal pole of the main axis, it is quite as characteristic of the 

 legion as the latter itself (see note A). The podoconus is primitively a vertical 

 regular cone, whose circular base occupies the horizontal jiorochora or " basal porous 

 area" of the central capsule, while its vertical axis coincides with that of the latter. 

 The apex of the cone, usually somewhat rounded off, is therefore directed towards the 

 aboral or apical pole of the central capsule and separated from it by a larger or smaller 

 interval In this interval the nucleus originally lies (as in PL 51, fig. 13 ; PI. 98, 

 fig. 13); but it is usually displaced subsequently and lies excentrically. The cone is 

 of very variable height ; on an average its vertical height is about equal to the diameter 

 of its horizontal base ; these dimensions are, however, dependent ujaon the form of the 

 central capsule ; the height being greater in slender ovoid or conical capsules, and 

 less in depressed sphseroidal or discoidal ones, than the diameter of the base. The 

 podoconus consists of differentiated endof)lasm, which becomes more deeply stained 

 by carmine and offers greater resistance to solvents than the surrounding finely granular 

 protoplasm. The apex, especially, becomes very intensely stained. It always exhibits 

 a very characteristic fine but distinct striatiou, numerous straight radial lines diverging 

 from the apex of the cone towards the base. The number of these strife appears to 

 correspond with that of the vertical rods in the j^oi'ochora, and each of these latter 

 stands apparently in du-ect communication with the basal end of an apical stria (§ 59). 

 These threads are probably differentiated constant contractile threads of endoplasm, or 

 even myophaues, comparable with the contractile cortical threads of the Cannopylea 

 and the permanent axial threads of the Actipylea. The numerous modifications, 



