SURFACE FAUNA OF THE GULF STREAM. 7 



through the vascular system ; and the terminal pouches of the liver are filled 

 Avith the brown granular mass usually considered to be a true liver. The 

 main tubes send off an endless number of fine ramifications (PI. IV, Fig. 14), 

 \\hich assume all possible shapes from that of a flat, angular pouch (PI. IV, 

 Figs. 11, 12 ; PI. V, Fig. 10), to an elongate, manj^-pointed star (PI. IV, Fig. 

 15), or to a tube bristling with fine projections (PI. IV, Fig. 14 ; PI. V, Fig. 

 8), which become lost in the thickness of the mantle. The ramifications 

 on the lower side of the mantle communicate with the reproductive indi- 

 viduals, as has already been seen by Vogt. 



The central polypite is large, whitish (PI. VI, Figs. 10, 11, 12, 13), with 

 strong interior longitudinal muscular bands, capable of great expansion and 

 contraction. It communicates at its base with the vascular system. Near 

 the aperture of the central polypite we find the extremity covered with 

 patches of small lasso-cells (PI. VI, Fig. 22), forming near its opening irregular 

 lips. The central opening is specially mobile. 



There are but few air-tubes (tubules) starting from the lower surface of 

 the float, and forcing their way through the liver to the base of the repro- 

 ductive polypites. The majority terminate as a single tube, and they rarely 

 ramifj^, as is stated to be the case by Krohn, in the Mediterranean species. 

 The air tubes vary greatly in number in different specimens. They take 

 their origin from the lower side of the float, in the five or six chambers 

 nearest the centre (PI. Ill, Figs. 18, 19, 20). They generally occur two or 

 three together, sometimes in tufts of four starting close together. They 

 sometimes branch, as has been described by Krohn,* but apparently not as 

 commonly as is the case in the Mediterranean species. The air tubes 

 extend through the liver in a more or less winding course (PI. III., Figs. 20, 

 21,) (but much more directly than in Porpita), and find their way to the 

 base of a few of the small feeding and reproductive polypites (PI. VI, 

 Fig. 19). In the only case where I have succeeded in tracing the termina- 

 tion of the air sac, it ended in a blind tube. The air tubes are arranged 

 much like those of Porpita, so that their course can be traced on the upper 

 side of the liver Avhen the float is removed and we examine the liver from 

 the upper side. The outer partitions of the interior chambers of the float, 

 where the air tubes take their origin, extend in a series of prongs and pro- 

 cesses (PI. Ill, Fig. 19) beyond the general surface of the float, so that the 

 rough walls of these inner chambers are in marked contrast to the smooth 

 outer walls of the other chambers of the float. 



* Archiv f. Naturg., 1848, I. p. 30. 



