REPORT ON THE SIPHONOPHOR^E. 261 



Palpacles (PI. XIX. fig. 1, r ; PI. XX. fig. 16, r). — From the upper face of the 

 proximal base of each palpon arises a very thin tasting filament, usually two or three 

 times as long as the palpon, but very extensible. It is usually described as an " accessoiy 

 tentacle," and represents a narrow cylindrical tubule with a very thin muscular wall, 

 distinctly articulated, like the antenna of a longicorn insect. The palpacles of the 

 living Discolabidse, quietly floating at the surface of the sea, are usually in a perpetual 

 feeling motion, undulating, tasting, and protruding in all directions. 



Gonostyles (PI. XX. figs. 11—16, q). — The corms of all Discolabidse are monoecious, 

 and their cormidia monoclinic, each possessing two gonostyles, a male and a female. 

 These are placed on the peripheral margin of the vesicular spiral trunk, between the 

 siphon and the palpon of each cormidium, the male (gh) below the female {(//)■ The 

 female gonostyle is placed beyond the palpon, richly branched, and forms in the 

 developed state an ovate bunch composed of many hundred subspherical clustered 

 gynophores. The male gonostyle (gh) is placed above the siphon, and is very different 

 in form. It is a single, very large, undivided palpon, with very contractile muscular 

 wall ; cylindrical in the expanded, slenderly pyriform in the contracted state. It- 

 is often elongated, hangs down like a tentacle, and is densely beset with numerous 

 oblongish or spindle-shaped androphores arising from short pedicles, either arranged 

 spirally or scattered irregularly. When the ripe androphores in the distal part of the 

 gonostyle are detached, their pedicles remain as short knobs or papillae (fig. 16, hp). 

 (Compare 27, Heft iii. Taf. v. figs. 9-15.) The umbrella of the gonophores is small or 

 rudimentary. The subspherical manubrium of the gynophores contains a single ovum 

 only, and is much smaller than the oblongish manubrium of the androphores. 



Ontogeny (PI. XIX. figs. 5—8). — The larva which arises from the fertilised egg of 

 the Discolabidse is a Siphonula, the helmet-shaped umbrella of which (b) includes a 

 pneumatophore (p) and has a deep ventral cleft. A large spindle-shaped siphon is 

 suspended in the bilateral cavity of the umbrella or bract, beyond the pneumatophore, 

 and at its dorsal side a tentacle, the tentilla of which bear each a simple subspherical 

 cnidal knob, very different from that of the adult Discolabidse. The development of this 

 medusiform larva from the fertilised eggs of Physophora magnified and its metamor- 

 phosis were observed by me in February 1867, in the Canary Island Lanzerote, and 

 described in my Entwickelungsgeschichte der Siphonophoren (84, p. 17, Taf. i.— iv.). 



The Challenger collection contained some larvae of Discolabidse very similar to these 

 iatter. The most remarkable are figured in PI. XIX. figs. 5—8. Fig. 5 represents a very 

 young Siphonula, the umbrella of which is nearly cap-shaped ; the siphon possesses no 

 tentacle, but some small buds of tentilla at its base. The larva, fig. 6, somewhat 

 older, has a large bract with a canal, some buds of palpons, and a long tentacle, beset 

 with a series of sessile cnidal knobs. These are replaced in the older larva, fig. 7, by 

 pediculate spherical cnidonodes, or larval tentilla ; the ventral cleft of the bract is much 



