REPORT ON THE SIPHONOPHOR^. 291 



The proboscis, the fourth and last segment of the siphon, is in the spirit specimens 

 examined usually short, highly contracted, and conical (PI. IV. figs. 19, 20, sr ; PI. VII. 

 fig. 42, sr). Often its proximal part is invaginated and turned over by the reflexed distal 

 part (PL VI. figs. 35, 37, 38, sr). Sometimes four or eight strong longitudinal muscle- 

 bands may be distinguished in the outer wall of the proboscis. The inner wall seems to 

 be beset with peculiar glandular cells. The distal mouth is usually highly contracted, 

 circular, with a thickened labial margin ; often it shows a circle of radial folds or lobes, 

 the number of which is sometimes four or eight, at other times twelve or sixteen (PI. VI. 

 figs. 35, 37, sr 1 ). 



Tentacles. — Each siphon bears in the Auronectse, as in all other Siphonanthae, a single 

 long tentacle, and this arises from the basigaster, near its basal part. As mentioned 

 above (p. 290) the tentacle remains attached to the basigaster, when the siphon becomes 

 separated from the cormidium by self-amputation (sudden contraction of the basal 

 sphincter), whereas the pedicle of the siphon remains attached to the corm. 



The tentacles of the Auronectse appear in two different forms, characteristic of the 

 two families of this order. The small Stephalidae (Stephalia, PI. VII., and Stephonalia, 

 PI. VI.) have simple, not branched tentacles, similar to those of the Apolemidaj and 

 Linop>hysa. The large Rhodalidae, however (Rhodalia, PI. III.; PI. IV. figs. 20-23), possess 

 branched tentacles, like the majority of Physonectae ; each tentacle bears a series of very 

 numerous tentilla or lateral branches ; in form and structure (fig. 23) they are very similar 

 to those of the Forskalidae. 



The simple tentacles of the Stephalidae are long and thin cylindrical tubules, and arise 

 from the dorsal side of the basigaster near its pedicle (PI. VII. figs. 39, 40). They are 

 usually very much contracted in the spirit specimens examined, and not much longer 

 than the siphons ; but in the expanded state and in the living animal they are probably 

 very long, several times longer than the whole corm. The tentacles of Stephalia (PI. VII. 

 figs. 39, 40) are all of the same size and similar form, not annulated, with equally disposed 

 cnidocysts. But Stephonalia (PI. VI.) possesses two different kinds of tentacles, larger 

 superior and smaller inferior. The thinner tentacles, much more numerous, agree with 

 those of Stephalia. The thicker tentacles, only developed in the proximal part of the 

 trunk, are far larger cylindrical tubules, and appear elegantly annulated when examined 

 by a weak lens ; each prominent annulus is composed of densely crowded cnidocysts, 

 wanting in the small constricted interval between each two rings (PI. VI. figs. 

 35, 37, 38, t). The distal part of these thicker tentacles has a peculiar structure; it 

 represents a cylindrical, articulated terminal filament, composed of about a dozen 

 segments, and bearing no annuli of cnidocysts (figs. 35, 37, tf). 



The branched tentacles of the Rhodalidae have a similar but more complicated 

 structure, and each bears a series of very numerous tentilla or lateral branches. The 

 cylindrical tube, which is 1 to 1*5 mm. in diameter, may reach in the fully expanded state 



