1572 THE VOYAGE OF H.M.S. CHALLENGER. 



up by air, when purified by hot mineral acids and afterwards dried, cannot be explained. 

 I suppose that the jelly contained in the cavity of the tubes remains in constant 

 connection by those openings with the jelly of the surrounding calymma. 



The distal ends of the radial tubes exhibit in the Aulacanthida the greatest variety in 

 the production of different branches and capturing apparatus, and this serves for the distinc- 

 tion of the genera and subgenera here described. In two genera only (in Aulactinium 

 PI. 101, figs. 68 ; and in Aulacantha, PL 105, fig. 16), the distal ends are simple, 

 not branched. In the four other genera they are armed with terminal branches, which 

 are usually arranged in elegant verticils. The greatest variety in the formation of these 

 verticils is developed in Aulographis (PL 103). The single branches of the terminal 

 verticils are here simple, whilst in the closely allied Auloceras they are forked or 

 elegantly ramified (PL 102). Aulospathis, the biggest of all Aulacanthida, is distin- 

 guished by the possession of a verticil of lateral branches, placed beyond the terminal 

 verticil, immediately above the veil of tangential needles (PL 104). Aulodendron , 

 finally, possesses lateral and terminal branches, which are irregularly scattered. 



The branches of the radial tubes are rarely straight, usually more or less curved, 

 either simple or again ramified. Their surface is either smooth or armed with small 

 spines or recurved teeth, often elegantly dentated or serrated (PL 103, figs. 2027 ; 

 PL 105, figs. 713). Their distal ends are either simply pointed or armed with a 

 spathilla, or a small crown of verticillate, usually recurved teeth (PL 104, figs. 417). 

 The variety and elegance of these minute armatures are very interesting, the more so as 

 they occur in very similar and analogous forms among the Aulosphaerida, the Ccelo- 

 graphida, and other PH^EODARIA. 



The central capsule of the Aulasphserida and its large nucleus (" Binnenblaschen "), 

 as well as the surrounding alveolate calymma (" Alveolen-Hiille "), and the enclosed 

 dark phseodium (" dunkles Pigment") were first described in my Monograph (1862, 

 loc. cit., p. 362). Their minute structure has been examined afterwards very accurately 

 by R. Hertwig (1879, loc. cit., p. 95). The numerous well-preserved preparations of 

 the Challenger (stained with carmine and preserved in glycerine) which I could examine, 

 confirmed in all respects the detailed description of Hertwig (compare PL 102, fig. 1 ; 

 PL 103, fig. 1; PL 104, fig. l). 



The spherical or subspherical central capsule is usually slightly depressed in the 

 shortened main axis. Its diameter is usually between O'l and '3, rarely less than 0'0& 

 or more than 0'4 mm. Its outer membrane (e) is thick and double-contoured, separated 

 by a clear interval from the very thin but firm inner membrane (i). The large 

 astropyle, or the main-opening on the oral pole of the main axis, is closed by a large, 

 convex, radiate operculum (o), from which arises a short tubular proboscis. On both 

 sides of the opposite aboral pole (to the right and left) are two conical parapyla? or 

 secondary openings (u, u). The space between the inner membrane of the capsule and 



