NECTOPHORES 



353 



-i- 0-5 mm. 



-J-0 



tO-5 mm 



- 1 - 



A b C 



Text-fig. 28. Physalia physalis. Three nectophores at different growth-stages. In A the gastrovascular space is wide open ; 



in C occluded. A, xyo,B, x 29, C, x 53. can.circ. 

 radial canal, lam.musc = muscular lamella. 



circular canal, can.ped.occl = pedicular canal (occluded), can.rad = 



view nothing more than the irregular folding of these tissues at the point where the radial canals arise 

 from the pedicel in the most advanced growth-stages that we know. It seems probable that the 

 nectophores must function as swimming-bells. 



Judging by the undoubted breaking-loose of the terminal branchlets, consisting of terminal 

 gonopalpon, nectophore and sexual medusoids, of Rhizophysa, I think it likely that the equivalent 

 sections in Physalia may do the same thing. In Rhizophysa, nectophore and palpon are orientated in 

 a peculiar way, axes in line, as if to balance each other when detached and swimming. In Physalia I 

 have seen some very expanded gonodendra in which the stalk separating this part of the branch from 

 the basal section — gonopalpon and jelly-polyp — is very fine. These terminal sections of the gono- 

 dendra, when detached, are probably kept on the move by pulsations of the nectophores. It may be 

 that the final branchlets become freed at some particular stage of growth, or at a certain season of the 

 year, but I must say that I have seen no specimens in which the nectophores are missing from the 

 normal position in which they first appear as very small buds very early in the development of the 

 gonodendron. 



Palpons 



(Pis. XX, XXV) 



Besides the gonophores and nectophores, the final parts of the gonodendra in Physalia are made up of 

 palpons (PL XX, fig. 4). The normal sub-terminal ones have at their base an asexual nectophore; the 

 palpons of the terminal sections have at their base a jelly-polyp (' Gallertpolypoid ' of Chun, a reduced 

 nectophore). None of the palpons have palpacles (simple tentacles). 



