SURFACE FAUNA OF THE GULF STREAM. 
on 
The large, exterior, marginal, prehensile tentacles (Pl. VI, Fig. 14) are 
S& 5) Ss ’ ’ g 
edged along the extremity with a band of lasso-cells, composed of large cir- 
cular cells, closely packed together (PI. VI, Fig. 15). Towards the base 
these bands of lasso-cells become disconnected (PI. VI, Fig. 17), forming 
g 
irregularly shaped disconnected circular patches (Pl. 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 polypites, 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 Porpitide, as identical with 
those of the Hydride Sertularide. The latter undoubtedly are to be so 
considered ; but the structure of the tentacles of Velella clearly shows that 
they are embryonic tentacles, analogous to the “Fanefaden” 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 Medusze buds already contain the peculiar yellow cells so 
characteristic of the free Meduse. Those which I have raised from Velella 
(PL. I, Figs. 15, 16) differ somewhat from that figured by Professor Agassiz 
(Contributions to the Nat. Hist. of the U.S., Vol. I, p. 53). On becoming 
free, the young Medusa (Pl. II, Fig. 10) has two rudimentary tentacles, one 
of which (¢) is somewhat longer than the other (/), which is in this stage 
a mere tentacular knob. The close resemblance of the Medusa at this stage 
with such Tubularian Meduse as Esuphysa, and Ectopleura is very striking. 
It has, like them, a row of large lasso-cells extending from the base of the 
tentacles (Pl. II, Fig. 14) to the abactinal pole (PI. We Figs? 10, 1 13); whe 
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., Pl. VII, Fig. 10. 1856. 
+ Mém. Inst. Nat. Génevois, I. 1853, Pl. II. 
