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



generally described as " tasters." It may, however, be possible, that they are originally 

 not palpons, but palpacles. In this case their morphological value would be different, as 

 is now assumed. They would be the dislocated tentacles, and not the manubrium of the 

 metamorphosed medusome, the umbrella of which is the nectophore. A proof of this 

 explanation seems to be given by the fact, that in Apolemopsis (according to the 

 accurate figure of Lesueur) a bunch of four tasting filaments arises from the base of each 

 nectophore. Kolliker (4, p. 19) and Leuckart (8, p. 317) state, that in Apolemia also 

 a bunch of three or four tasters belongs to each single nectophore. 



Pneumatophore. — The float filled with air is relatively small in the Apolemidse, 

 compared with the large nectophores. It has a very simple structure, as in the oldest 

 and lowest forms of Pkysonectas. The ovate pneumatosaccus (which sometimes 

 contains no pneumatocyst ?) is a simple invagination of the apex of the tubular trunk. 

 The inflated pyriform uppermost part of the latter, or the pneumatocodon, which 

 loosely surrounds the pneumatosac, is not connected with it by vertical radial septa (as 

 is constantly the case in the Agalruidse and Forskalidag). There is wanting, therefore, in 

 the Apolemidae the corona of radial pouches which is characteristic of the pneumatophore 

 in the two latter families. The spheroidal basal or lowermost part of the pneumatosac 

 — -the pneumatic infundibulum, or the gas-secreting gland, pneumadenia — is separated 

 from its ovate larger upper part by an incomplete annular constriction, the pneumato- 

 pyle (pylorus infundibuli). (Compare 50, p. 272, Taf. xix. fig. 93.) 



Nectophores. — The large and vigorous nectocalyces of the Apoleruidas have a some- 

 what different shape in the two subfamilies. The two opposite nectophores of Dicymba 

 (PI. XVIII. fig. 1) resemble those of Praya (PI. XXXI. figs. 1-7). They are ovate, 

 with a rounded and edgeless exumbrella, and bear at the ventral or axial side a large 

 longitudinal furrow, bounded by two parallel wings ; between these wings there arises 

 in the upper part the lamellar triangular pedicle, which attaches the nectophores to the 

 top of the stem, beyond the pneumatophore. The two ventral grooves of the two 

 opposite nectophores, the larger of which embraces the smaller, form together a 

 hydrcecial canal, in which the siphosome may be partly retracted. Apolemia bears to 

 Hip>'popodius much the same relation as Dicymba exhibits to Praya. The large ventral 

 groove of each nectophore here embraces a corresponding part of two obliquely opposite 

 nectophores, a superior and an inferior (compare 8, p. 314). The form of the umbrella 

 is similar to that of Hippopodius, and so also is the arrangement in the biserial 

 nectosome. The mouth of the nectosome is relatively small, and directed downwards 

 and outwards. The four radial vessels of the powerful subumbrella, connected by a 

 small ring-vessel above the insertion of the velum, are strongly differentiated. The two 

 sagittal canals (shorter ventral and longer dorsal) make a simple curve in the median 

 plane of the nectophore, whereas the two lateral canals (right and left) are much 

 prolonged and have a complicated course, with two to four undulate turnings ; from the 



