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



7. All the parts which arise by budding from the primary larva of the 

 Siphonophorse are either medusiform persons or special organs of the same. 



8. All organs which belong originally to one medusoid person are included in the 

 definition of a Medusome, whether they bud out from a common basis on the stem, or 

 arise in different positions, in consequence of kenogenetic migration or dislocation ; the 

 multiplication of individual equivalent portions (e.g., nectophores, bracts, palpons) ' which 

 often occurs secondarily is simply to be regarded as a multiplication of organs, not of 

 persons or medusomes. 



9. The medusomes appear on the Siphonophoral colony in two distinct main forms, 

 which cannot however be sharply distinguished — in the palingenetic medusomes the 

 principal organs have remained more or less in their original connection (e.g., in the 

 gonophores of Eudoxia); in the kenogenetic medusomes, on the other hand, the 

 principal organs are more or less dislocated, e.g., in the sterile medusome of Eudoxia, 

 which consists of a protective piece (umbrella) and a gastral tube (siphon) with a tentacle. 



10. The lateral budding of the secondary medusomes (appendages) on the Siphono- 

 phoral stem occurs sometimes singly and sometimes in groups. Those groups which 

 consist of several medusomes we call " cormidia." 



11. The cormidia are originally simple segmental repetitions of a medusome-group 

 in metameric succession separated by free internodes (cormidia ordinata), e.g., the 

 Eudoxise of the Calycophoridae, the Prodoxise of the Physophoridae (Apolemia, &c). 



12. By the breaking up of such original cormidia, those centralised cornis arise 

 in which the persons bud in a scattered fashion over the stem, their several organs thus 

 becoming separate from one another (cormidia dissoluta), e.g., Agalmoptsis, Rhizophysa. 



13. The degeneration of the single medusomes and of the disassociated organs is of 

 the greatest importance in the development of the Siphonophoral colonies, and that the 

 more, the more markedly the corm is centralised and the more intimate the mutual 

 relations between the polymorphic medusomes. 



DISCONULA LARVA of the DISCONANTHiE. 



Among the different medusiform larvae of Disconanthae (Chondrophoridse or 

 Porpitariae) which I was able to observe, the youngest larvae of Porpitidas (from 0"1 to 

 0*4 mm. in diameter) are of special importance. They possess a circular, flatly arched 

 disc, the margin of which bears a circle of eight simple tentacles. From the middle 

 point of the subumbrella hangs a large central gastral tube, and from the base of this 

 siphon arise at equal distances eight radial canals, which run in the concave subumbrella 

 to the margin of the disc, and are there united in a circular canal. Above this there 

 lies in the middle of the gelatinous disc a pneumatophore, composed of a central lens- 

 shaped air-flask and a circle of eight radial air-chambers surrounding the same. Both 



