240 THE VOYAGE OF H.M.S. CHALLENGER. 



a hundred thousand. The form and size of the bracts are extremely variable and usually 

 more or less irregular ; their arrangement is very difficult to recognise, since they are 

 hyaline and easily detached. Usually they have the form of oblongish scales, with 

 concave lower and convex upper face ; the latter bears often three to five dentate ribs 

 or crests. The bracteal canal is always simple and runs along the lower face. The 

 great variety in size and form of bracts, in one and the same specimen, is exhibited 

 by figs. 10 to 18 of PI. X. 



Siphons. — The polypites of the Forskalidse are very large and highly developed, 

 and sometimes of an extraordinary size. The spindle-shaped siphons of Bathyphysa are 

 larger than those of any other Siphonophorse hitherto known ; they attain (in a strongly 

 contracted state) the length of 50 to 60 mm. and the thickness of 30 mm., and are 

 attached by pedicles of 200 mm. in length. But even in the smaller species of this 

 family the siphons and their pedicles attain a considerable size. The thin tubular 

 pedicles are usually covered with numerous bracts, in manner similar to the trunk of 

 the siphosome. The three parts of the siphon proper are usually well developed 

 (PI. IX. figs. 7-9). The thick-walled basigaster, with masses of cnidocysts, is sometimes 

 divided by four longitudinal furrows into four equal quadrants. The wide stomach 

 bears usually eight, twelve, or sixteen longitudinal liver-ridges, coloured brown or red ; 

 these are wanting in Bathyphysa, being replaced by innumerable small hepatic villi 

 (similar to those of Athorybia). The muscular proboscis is very strong and extensible, 

 and provided with a widely expansible mouth. The opening of the mouth is often 

 surrounded by a corona of eight or sixteen short lobes. 



Tentacles. — The form and structure of the single large tentacle which is attached 

 to the base of each siphon seems to be the same in all Forskalidse. The point of 

 insertion is in the constriction between the basigaster and the distal end of the long 

 pedicle (PL IX. figs. 7 , 8). The number of equidistant tentilla or lateral branches, 

 which are inserted in the nodes of the regularly segmented tentacle, is very large. 

 Each tentillum (PI. X. fig. 23) has a long pedicle (ts), a large spiral cnidoband (tk), and 

 a long terminal filament (tf). The number of the spiral turnings of the naked cnido- 

 band, which is not enclosed by an involucre, is variable in the single species, usually 

 two, three, or four. Its colour corresponds to that of the siphon (usually red). The 

 broad spiral riband is composed of many series of innumerable small paliform cnidocysts, 

 and of two simple lateral series of large ensiform cnidocysts (fig. 23, tk). 



Cystous. — All Forskalidse possess a great number of hydrocysts or spindle-shaped 

 vesicles, which are attached to the base of the siphons in Strobalia, whilst they are 

 inserted into the trunk of the siphosome, between the siphons, in the three other genera. 

 They are usually described as " tasters." An accurate examination of them, however, 

 shows that three different forms of them must be distinguished, viz., cystons, palpons, 

 and gonopalpons. The two former bear a palpacle, wanting in the latter. The cystous, 



