REPORT ON THE S1PHONOPHOR.E. 33 



unite in the centre of its upper face, forming a'typical octoradial " liver star." This is 

 quite regular in the youngest Discalidse and Porpitidse ; it is amphithect in the young 

 Velellidae, where the two opposite canals of the sagittal axis are larger than the six 

 others, three right and three left (compare Bedot, 60, pi. ix. figs. 1, 2). 



These eight primary liver-canals, running between upper face of the centradenia and 

 lower face of the pneumatosaccus, must be regarded originally as ascending branches of 

 the eight primary radial canals of the subumbrella, which run from the basigaster towards 

 the peripheral limb. All the numerous canals (partly hepatic, partly renal vessels) which 

 traverse the centradenia of the larger Disconectaa in all directions, and form a complicated 

 network, are merely secondary branches and ramifications of those eight superficial canals 

 of the primary " liver-star." They seem to be disposed and differentiated in a variable 

 manner. The majority of Disconectae exhibit in the adult state a superior system of 

 hepatic vessels (characterised by production of brown or blackish pigment granules) and 

 an inferior system of renal vessels (characterised by the production of greenish guanin- 

 crystals), the so-called " white plate " of its discoverer, Kolliker. 1 



The cnidoblasts and the intermingled matter, indifferent or interstitial cells of the 

 exoderm, which, densely aggregated, constitute the solid glandular parenchyma of the 

 centradenia, doubtless have their origin in the exoderm. But the locality of their origin, 

 or the point of their exit between the central siphon and pneumatosaccus, has hitherto 

 been doubtful. Bedot, who has given the best and most accurate histological description 

 of the " central organ" of the Velellidge (58-61), assumes that the place of their origin 

 is the subumbrella. According to his description, 2 a number of subumbral exoderm-cells 

 immigrate into the interior, passing through numerous pores of the subumbrellar support 

 (his " lamelle aniste externe," he. cit.). These pores possess, in my opinion, a secondary 

 importance, and are perhaps artificial openings. 



It seems to me much more probable that the exodermal cells of the centradenial 

 parenchyma may be derived from the basal or inferior part of the pneumatosaccus, i.e., 

 that invaginated lamella of the exumbrellar exoderma which encloses and produces the 

 chitinous pneumatocyst (" couche cellulaire qui tapisse le pneumatophore " 3 ). This 

 important part of the pneumatosac is, in young Disconectse, in immediate contact with 

 the upper face of the centradenia, as Bedot himself has demonstrated. 4 The structureless 

 support, which separates the two organs in the adult (" lamelle aniste interne " of Bedot, 

 he. cit., p. 238), is not yet formed. This, in my opinion, is right, and the constituting 

 exodermal cells of the centradenial parenchyma are derived from the exumbrellar invagina- 

 tion of the pneumatosaccus ; they may be compared to the glandular gas-secreting cells 

 of the " infundibulum pneumatophori " of the Siphonanthas. I have very often found in 

 well-preserved specimens the cnidoblasts of the centradenia filled with an air-bubble, and 



1 Kolliker, 4, p. 59. 2 Bedot, 59, p. 503, pi. xxv. figs. 4 le, 8 o. 



3 Bedot, 59, pi. xxv. figs. 4, 5 in. * Bedot, 60, p. 238, pi. ix. fig. 2. 



(ZOOL. CHALL. EXP. — PAET LXXVII. — 1888.) HMh 5 



