REPORT ON THE SIPHONOPHOR^E. 241 



anal or excretory vesicles (PL X. fig. 19), differ from the two other forms in the 

 possession of a terminal opening. They are much smaller than the siphons, and without 

 hepatic ridges, but exhibit a similar composition of four different segments ; a basal 

 pedicle (fig. 19, qp), a thick -walled hemispherical basigaster, at the base of which is 

 inserted the single long palpacle (r), a large thin-walled stomach (q), and finally a 

 conical or pyriform chromadenia, with a distal opening. This latter segment, which is 

 comparable to the proboscis of the siphons, is most characteristic of the cystons ; it is a 

 colour -gland, which produces a great mass of pigment -granules, and extrudes it through 

 the terminal anus. The dark glandular entoderm of the chromadenia is much thicker 

 than the colourless entoderm of the thin-walled stomach ; the pigment-granules secreted 

 by it are usually red or brown, sometimes intermingled with small crystals. When a 

 quietly floating Forskalia is touched, it suddenly discharges the contents of the 

 chromadenia, and makes the surrounding water dark and intransparent. Kolliker 

 (4, p. 8) and Leuckart (5, p. 17, and 8, p. 348) have already described this interesting 

 excretion ; but they suppose that there is no true opening at the distal end of the 

 cystons, and that the pigment is discharged by rupture of their wall. Repeated 

 observations on the living Forskalia tholoides have convinced me that the pyriform 

 red chromadenia, or the opaque distal portion of the cyston, possesses a constant 

 terminal opening. This anus or excretory opening, however, is difficult to observe in 

 the closed state (as is also the case in the mouth and the anus of many lower animals). 

 The opening has been observed too by Studer in the cystons of Bathyphysa abyssorum, 

 which he has described as bracts (40, p. 20). The excretion of the pigment-masses and 

 the darkening of the water by it have probably the same physiological function as in the 

 Cephalopoda ; — to protect the attacked animal from its persecutors, and facilitate the 

 capture of food-animals. 



Palpons. — Whilst one cyston only belongs to each cormidium of probably all 

 Forskalidse, the number of true palpons (formerly confounded with the cystons) is 

 usually much larger. In Forskalia there belong usually two palpons (arising from a 

 common pedicle) to each cormidium, in Forskaliopsis three, four, or more ; in some of 

 the largest forms a pediculate bunch of four to six or more palpons arises from the 

 trunk between each siphon and the appertaining cyston. The true palpons differ from 

 the latter mainly in the absence of a distal opening ; they are closed at the pointed 

 distal end, and communicate only by the pedicle with the tube of the trunk. Their 

 size is usually about half that of the siphons and cystons, but very variable according 

 to the different state of contraction. Sometimes the palpons are simple pyriform or 

 spindle-shaped vesicles, at other times divided by an annular constriction into a 

 smaller proximal and a larger distal part. The pointed apex of the latter is usually 

 provided richly with larger cnidocysts and long sensitive cnidocils, sometimes also 

 coloured by pigment. Their function is sensory. The long palpacle which arises from 



(ZOOL. CHALL. EXP.— PAUT LXXVII. — 1888.) Hhhh 31 



