REPORT ON THE STPHONOPHOR^E. 219 



only a single one or a group of two. The palpons are united in a bunch, attached 

 to the basal insertion of the siphon, in the ordinate corrnidia of the Stephanomidse ; they 

 are isolated, attached immediately to the trunk, and scattered between the siphons, in 

 the dissolved corrnidia of the Halistemniidse ; sometimes their succession is regular, at 

 other times irregular. Usually one palpon (or cyston) is in direct connexion with the 

 gonodendra, whilst others are independent of them. The palpons are thin-walled, 

 cylindrical, very contractile and movable tubes, closed at the distal end, which is armed 

 with thread-cells. Sometimes the distal part of the palpon is separated by an annular 

 constriction and forms a subspherical cavity, in which a group of crystals or concretions 

 (like an otolith) is turned round by the ciliated entoderm, as in an otocyst. 



Cystous. — Hydrocysts with a terminal mouth opening, or cystons, occur very 

 frequently (perhaps even constantly ?) in the Agalmidaa ; they were formerly confounded 

 with the similar mouthless palpons. They are larger than the latter, with a thicker 

 entoderm, which is partly glandular, and often coloured (red or brown). The fluid 

 secretion, or the pigmented, granular or crystalline masses secreted by it, are ejected 

 by the distal mouth, or rather the anal opening, which is closed by a muscular sphincter. 

 Sometimes the distal part is separated from the dilated middle part by an annular 

 constriction (PI. XV. figs. 8, 9). I have never found more than a single cyston in each 

 cormidium, whilst the number of palpons is usually large and variable. 



Palpacles. — Many Agalmidae, but not all, possess a number of long and thin palpacles, 

 feeling or tasting filaments. Usually a single palpacle (or " accessory tentacle ") is 

 attached to the base of each palpon and probably also of each cyston. But in some 

 species they have not been described ; possibly they were either overlooked or lost 

 accidentally. Each palpacle is a very slender cylindrical tubule, the muscular wall of 

 which is very expansible and contractile, the cells of the exoderm covered with palpocds 

 and partly containing small cnidocysts. 



Gonostyles. — All the Agalrnidae have monoecious corms and monoclinic corrnidia; each 

 cormidium possesses a male and a female gonodendron. These arise sometimes from a 

 common pedicle, at other times separated from two neighbouring gonostyles. The 

 ordinate corrnidia of the Stephanomidse always bear a small pair of gonostyles, a male 

 and a female, attached to their common trunk near the siphon. The loose corrnidia 

 of the Halistemmidas, however, exhibit a variable arrangement. Sometimes a monoclinic 

 pair of gonodendra, united with a palpon or cyston, arises from each internode, midway 

 between two neighbouring siphons ; at other times each internode bears two to four or 

 more pairs of gonodendra ; and sometimes their disposition is quite irregular, numerous 

 male and female gonodendra being scattered irregularly along the whole trunk of the 

 siphosome. Usually the gonodendra are small clusters, and their gonostyles simple or 

 little branched. The female gonophores are smaller and more numerous than the male. 

 Their umbrella is usually well developed, pedunculate, but sometimes rudimentary. 



