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



The family Discolabidse comprises those polygastric Physonectse, the nectosome of 

 which is well developed, with a long trunk and two or more series of nectophores, whilst 

 the trunk of the siphosome, without bracts, is shortened and subhorizontally expanded 

 in the form of a wide spiral bladder, the ventral periphery of which bears a series of 

 ordinate cormidia, protected by a corona of large palpons. 



The well-known type of this family is the Mediterranean Physophora hydrostatica, 

 figured and described in 1775 by Petrus Forskal. Its accurate anatomical description 

 was given in the years 1853 to 1860 by Kolliker (4), Vogt (6), Gegenbaur (10), and 

 Glaus (34). Huxley (9) established for this genus the family Pkysophoriadse and gave to 

 it the following definition : — " Physophoridse with nectocalyces, but without hydrophyllia. 

 The distal end of the filiform "ccenosarc dilated. Tentacular branches with involucrate 

 sacculi. Pneumatocyst small." The name Physophoridae for this family has also 

 been retained by later authors ; but unfortunately it is employed with no less than 

 four different meanings, and therefore has lost all value (compare above, p. 186). It 

 may be, therefore, best to call this family Discolabidse, from another genus belonging 

 to it, Discolabe (Eschscholtz, 1, p. 155). A third genus is Stephanospira of Gegenbaur 

 (10, p. 67). 



Nectosome. — The swimming apparatus of the Discolabidse is composed of numerous 

 large nectophores, arranged in various ways around the vertical tubular trunk, and of 

 an apical pneumatophore at the top of the common trunk. Usually (in the typical 

 Physojihora) the nectosome is biserial {disticha), as in the Agalrnidas, composed of two 

 opposite longitudinal rows of nectophores (usually four to six pairs). Discolabe differs 

 in having a quadriserial nectosome (tetrasticha), similar to Sphyrophysa ; it is composed 

 of four cruciate longitudinal series of nectophores (or of four to six quadriradiate coronas). 

 Stephanospira, finally, has a conical or multiserial nectosome (polysticha), similar to that 

 of the Forskalidas ; the nectophores are here very numerous and arranged in a long 

 continuous spiral, with four to six or more turns. The trunk of the nectosome, after 

 the detachment of the nectophores, is a cylindrical, or in the contracted state, spindle- 

 shaped bladder, which bears on its ventral side a lamellar longitudinal fold, like a 

 mesentery, and at the free edge of this a series of spirally convoluted folds, the 

 insertions of the detached nectophores. The tapering proximal end of the vertical 

 spindle-bladder is separated by a constriction from the pneumatophore, and the broader 

 distal end by a similar constriction from the inflated trunk of the siphosome (PI. XX. 

 figs. 9-12). 



Pneumatophore (figs. \,p, 9-13, p). — The float filled with air has in the Discolabidse 

 the same structure as in the Agalmidse. It is ovate or subcylindrk-al, with a red 

 pigment-spot at the apex, and with a variable number (usually eight) of longitudinal ribs 

 in the outer wall. These arise in the lower half as eight (more rarely seven or nine) 

 vertical radial septa, which connect the inner with the outer wall and divide the 



