3 o DISCOVERY REPORTS 



developed in the larva precociously (by heterochrony). It was then developed still further in the 

 adult for the same purpose (swimming). Some adult Physonects took to swimming by jet propulsion, 

 it might almost be said, because of an ' afterthought ' on the part of an ancestral larva. 



The old suborder Disconanthae contains three forms Velella, Porpita and Porpema that are really 

 the floating Tubulariid hydroid-phases of inconspicuous adult Codonid medusae known as Chryso- 

 mitra. There is nothing in their morphology in the least like the Siphonanthae, and it is possible that 

 their pneumatophore has been acquired independently. They form a separate Order Chondrophora. 

 Garstang (1946) interpreted the Conaria larva, but omitted reference to important papers by Delsman 

 (1923) on the Conaria larva of Porpita and its development, and by Leloup (1929), who, after studying 

 Velella at Villefranche, pointed out the homology between the Conaria larva and the actinula of 

 Tubularia larynx, showing that the peculiar ' crimson cone ' of Conaria corresponded with the ' gastric 

 diaphragm' of Tubularia. This work of Leloup appears not to have been known to Garstang. 



Flrud 



-Tlarv. 



Text-fig. 6. A, Actinula of Tubularia. After Leloup (1929). B, Conaria of Porpita. Based on 

 Delsman (1923, figs. 16, 17, 18). X Y= homologous planes. 



Text-fig. 6 will make this point clear. There is no need to endeavour, as Garstang did, to 'close 

 the gap ' between Disconanths and Siphonanths. The old order Siphonophora without doubt had 

 a double origin, as Haeckel realized. 



As to the position of Pelagohydra, one is struck by the origin of the tentacles between the axial 

 parenchyma in the meshes between the endoderm canals, from which the gonophores (gonozooids 

 now reduced) spring. In Chondrophora Bigelow's sections show that the tentacles arise from the 

 canals themselves. The difficulty of exactly homologizing the structure of the two forms was stressed 

 by Garstang (1946, p. 126), and of course Pelagohydra has no pneumatophore. Garstang maintained 

 that the ' float ' of Pelagohydra represents the hydrocaulus of Corymorpha, on account of the position 

 of the gastric diaphragm, and that the gonophores are cauline. In the Chondrophora the gonophores 

 are on the oral cone. Possession by hydroids of cauline gonophores is probably a later evolutionary 

 stage than that of oral ones and in the opinion of my colleague Dr W. J. Rees leads on to a hydrorhizal 

 position. 



The Chondrophora appear to be aberrant, pelagic, tubularian Anthomedusae. They have lateral 

 (radial) extensions of the walls of the aboral chamber, the edge of the extension being provided with 





