SURFACE FAUNA OF THE (JULF STREAM. 5 







The large, exterior, marginal, prehensile tentacles (PI. VI, Fig. 14) are 

 edged along the extremity ^vith a band of lasso-cells, composed of large cir- 

 cular cells, closely packed together (PI. YI, Fig. 15). Towards the base 

 these bands of lasso-cells become disconnected (PI. VI, Fig. 17), forming 

 irregularly shaped disconnected circular patches (PI. VI, Fig. 16). In young 

 tentacles these bands of lasso-cells are not clearly defined, and when they first 

 make their appearance they appear as patches near the base, gradually ex- 

 tending towards the extremity, there to form the connected bands of the 

 older tentacles. The large prehensile tentacles, the feeding and reproduc- 

 tive polj-pites, are all attached to the lower side of the space occupied by the 

 float, and to the part of the mantle immediately adjoining it. Huxley consid- 

 ers the tentacles of Velella, as well as those of the Porpitida), as identical with 

 those of the Hydridse Sertularidaj. The latter undoubtedly are to be so 

 considered ; but the structure of the tentacles of Velella clearly shows that 

 they are embrj^onic tentacles, an.alogous to the "Fangfaden" of Physalia, and 

 of other Siphonophores, in which the lasso-cells are arranged in the most sim- 

 ple form, as bands along the edge ; while in Physalia they form the peculiar 

 well-known reniform appendages paved with large lasso-cells. It is difficult 

 in Velella and Porpita to distinguish the young polypite from the hydrocysts 

 of other Siphonophores, and they do not appear to be present in those genera. 



The small Medusae buds already contain the peculiar yellow cells so 

 characteristic of the free Medusae. Those which I have raised from Velella 

 (PI. II, Figs. 15, 16) differ somewhat from that figured by Professor Agassiz 

 (Contributions to the Nat. Hist, of the U. S., Vol. HI, p. 53). On becoming 

 free, the young Medusa (PI. II, Fig. 10) has two inidimentary tentacles, one 

 of Avhich {t') is somewhat longer than the other {t), which is in this stage 

 a mere tentacular knob. The close resemblance of the Medusa at this stage 

 with such Tubularian Medusae as Esuphysa, and Ectopleura is very striking. 

 It has, like them, a row of large lasso-cells extending from the base of the 

 tentacles (PI. II, Fig. 14) to the abactinal pole (PI. II, Figs. 10, 11, 13). The 

 yellow cells are arranged in clusters along the sides of the four broad chymi- 

 ferous tubes (PI. II, Figs. 10, 11), as well as on the surface of the short, 

 rounded, conical, rudimentary proboscis. The Medusa of Velella figured 

 by Gegenbaur * has eight chymiferous tubes and one large tentacle ; that 

 figured by Vogt,t on the contrary, has only four chymiferous tubes, but 



» Zeits. f. Wiss. Zool. VIII., PI. VII, Fig. 10. 1856. 

 t Mem. Inst. Nat. G^nevoia, I. 1853, PI. II. 



