6 SURFACE FAUNA OF THE GULF STREAM. 



eight rows of yellow cells, two on each side of the broad tiibes, which may 

 have misled Gegeiibaur. The Medusfe buds figured by KiiUiker* agree with 

 the younger stages as figured by Vogt. The Medusa, when it first becomes 

 free, is elongate, somewhat conical at the abactinal pole. After a couple of 

 days the outline becomes flattened and more hemispherical (PI. II, Fig. 11). 

 The young Medusse move with considerable activity by sudden jerks, like 

 some of the Tubularian Medusae. The tentacles did not increase in length 

 during the time they were kept in confinement (ten days); nor did I fish up 

 any others more advanced than those here figured (PI. II, Fig. 11) during 

 my stay at the Tortugas. 



Kiilliker has given an excellent account of the course of the so-called liver 

 system in the Mediterranean species. I have been able to trace, as he has 

 done, its ramifications through the mantle, over its free surface (PI. IV, 

 Fig. 14; PI. V, Fig. 8), extending beyond the float (PI. IV, Figs. 8, 11), to 

 the edge, as well as the ramifications extending over the float and the sur- 

 face of the keel (PI. V, Figs. 1, 2, 4, 5). In addition to the two main 

 branches of the system extending round the edge of the keel from the base 

 of the float (PI. V, Figs. 4, 5, v„), there are two other large branches, which 

 run across the float in the deep groove (PI. Ill, Figs. 3, 14, 15, 17./.), running- 

 oljliquely across it. These two branches run up on each face of the keel 

 (PI. IV, Fig. 15. V ; PI. V, Figs. 1, 2. r) from the float, and then anastomose 

 with the main branches described by Kiilliker. All along their course, from 

 the fixed edge of the mantle to the main branch running about jDarallel to the 

 edge of the keel, the main branches give off a system of meshes and branches 

 which cover the whole of the float and keel, and anastomose (PI. IV, Fig. 5 ; 

 PI. V, Figs. 1, 2, 3, 4) with those extending over the mantle from the fixed 

 edge of the mantle to its periphery. The secondary branches, forming the 

 free edge of the mantle of the keel, which are given off fi cm the main margi- 

 nal branch, send off short simple secondary branches at right angles to the 

 primaries, thus forming a sort of frill. The extremity of these tubes, again, 

 is connected by a small marginal canal (PI. V, Figs. 4, 5). The so-called 

 liver t is suspended from the lower side of the -float, running up into its 

 conical portion (PI. V, Fig. 11). The main longitudinal branches (PI. V, 

 Figs. 11, 12, 1.3.?) give rise to all the finer ramifications which extend through 

 the whole thickness of the mantle. Fluids circulate with great rapidity 



* Die Si;hwimmpol)r[)en von Messina. 1853. 



t In Velellaand Porpita tbe hepatic organ, as has heen pointed ont hy Huxley, occupies the same posi- 

 tion witli regard to tlie pneuuiatocyst which it occnpies in Rhizophysa. 



