REPORT ON THE SIPHONOPHOR^E. 37 



dilated basal part. Sometimes the proximal half, or the stomach, is separated by 

 a constriction from the distal half or the proboscis. The upper or proximal half only 

 produces by budding the numerous medusiferous gonophores, whilst the distal part, or 

 the contractile proboscis, is armed with cnidonodes. The wall is very contractile, since 

 the longitudinal muscles of the exoderm and the circular muscles of the entoderm are 

 not less developed than in the large central siphon. Sometimes the wall of the gono- 

 styles exhibits eight longitudinal folds or ribs ; and often, too, the patches of cnidocysts 

 (or the cnidonodes) are arranged into eight parallel longitudinal rows along the 

 proboscis. 1 



The gastral cavity of the gonostyles opens above into a canal of the subumbrella, or 

 of the centradenia. Its lower or distal end is a closed caecum in the monogastric 

 Discalidae, the terminal apex being densely beset with cnidocysts. It opens by a terminal 

 mouth in the Porpitidse and Velellidae ; this mouth is not less contractile and expansible 

 than the larger mouth of the central siphon. Often the former exhibits four cruciate 

 lips, more rarely eight ; sometimes it is circular, without mouth lobes (compare the 

 descriptions of the gonostyles by Kolliker (4), Vogt (5), Leuckart (8), Huxley (9), 

 Agassiz (57), and others). 



Gonophores. — The medusiform gonophores arise from the proximal part of the gono- 

 styles, rarely isolated, usually crowded in smaller or larger groups or bunches. They are 

 in all Disconectae of the same form, and are detached from the budding gonostyle before 

 coming to sexual maturity. The detached gonophores are very small quadriradial 

 Medusae of very simple structure. Their subumbrella exhibits four regular radial canals 

 which unite above the velum by a circular canal (compare the above-mentioned authors). 



Tentacles. — The limb of the umbrella is in all Disconectae armed with a corona of 

 tentacles, in the same manner as in all fully-developed Hydromedusae. They are placed 

 not at the margin itself, but more or less inside, at its lower face, the peripheral zone 

 of the subumbrella. They are, therefore, strictly speaking, submarginal tentacles (such 

 as occur also in some Medusae, e.g., Drymonema). Some authors (Glaus, Alexander 

 Agassiz, &c.) regard these organs as self-subsistent persons or zooids, and call them 

 " prehensile polypites," " marginal polypites," " tasters," " dactylozooids," &c. But this 

 conception is quite erroneous, and, in my opinion, there can be no doubt that the sub- 

 maro-inal corona of tentacles in the Disconectae are the same organs as in the common 

 Medusae, both from a morphological and from a physiological point of view. 



Octoradial Corona of Tentacles. — It is a most important fact, not hitherto pointed out 

 as it deserves, that in the larvae of most Disconectae there occurs a typical stage, with a 

 corona of eight equidistant and regularly disposed tentacles. They are placed at the 

 distal end of the eight primary radial canals which arise from the base of the central 

 siphon, run along the subumbrella, and are connected round the margin by the circular 



1 Compare 57, pi. ii. figs. 1-8. 



