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



tentacle. Nectosome biserial, with two opposite rows of nectophores. Pneumatophore 

 with radial pouches (compare Pis. XIV.-XVII.). 



The family Agalmidas, the largest of all Physonectae, comprises those polygastric 

 " Physophoridas " which possess a biserial nectosome, and at its apex a pneumatophore 

 with radial pouches; the long tubular stem of the siphosome bears numerous siphons, 

 bracts, and palpons ; the tentacles are always branched, with a single series of tentilla. 



The genera and species of Agalmidse are rather numerous, and widely distributed over 

 all seas ; they occur in the Arctic as well as in the temperate zones, but mostly in the 

 Tropics. The majority, however, occur only at certain seasons and not in great numbers; 

 nearly all are extremely delicate and sensitive, and the component parts easily detached 

 from the stem. Most of the older observers, therefore, have only described fragments 

 or single isolated pieces. A further great obstacle to accurate examination is the 

 extraordinary mobility and contractility of most Agalmidse. 



The first figures and descriptions of Agalmidse were given by Peron and Lesueur (14, 

 Stephanomia, 1807), and by Eschscholtz (21, Agalma, 1825). Lesson (3, 22) and Quoy 

 and Gaimard (2, 19, 20) published figures and descriptions of numerous scattered pieces, 

 but without great value. Brandt in 1835 described Agalma mertensii from an excellent 

 (though alas unpublished) figure by Mertens (made in 1827), and founded upon it the 

 family Agalmidse (25). Sars in 1846 published accurate figures of the northern Agalmopsis 

 elegans. The excellent observers in the sixth decade of our century (1853-1859), 

 Kolliker (4), Vogt (6), Leuckart (5, 8), Gegenbaur (7, 10), and Huxley (9), greatly advanced 

 our knowledge of the Agalmidse, which were also called Stephanomidse (including 

 Forskalia). Some new interesting species have been described recently by Claus (74, 

 75), Fewkes (42-45), &c. In general, however, there yet remains much to be done towards 

 a more accurate knowledge of this important and interesting family. 



My own observations on numerous different Agalmidas were commenced in 1859 in 

 Messina, and continued in the winter of 1866-67 in the Canary Islands; but the richest 

 harvest was found during my residence in Ceylon, where I had the opportunity of observing 

 several new and interesting forms. The Challenger collection contained many isolated and 

 scattered portions of detached parts of Agalmidas, but no complete specimens of any value. 



Nectosome. — The swimming apparatus of the Agalmidas is composed of a small apical 

 pneumatophore and of two opposite rows of large alternating nectophores. These are so 

 arranged around the axial trunk, that the apical part of each nectophore fits into the 

 interval between two neighbouring nectophores of the opposite row, a superior and an 

 inferior. The trunk itself, therefore, is spirally twisted, since the insertions of all the 

 nectophores originally form a single straight series in the ventral median line of the trunk. 

 The spiral line usually is lseotropic (or a lambdoid spiral), therefore opposed to the spiral 

 of the siphosome, which is (perhaps always) dcxiotropic (or a deltoid spiral). The number 

 of nectophores is in most species ten to twenty, but in some smaller forms only four 



