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



The buds or the secondary sporosacs contain either a single large ovum or a group 

 of several small ovules ; they have usually a long pedicle, and its canal arises from the 

 base of the primary spadix. 



The different remarkable modifications of gonophores here enumerated, exhibited in 

 the adult spirit specimens examined, showed no regular distribution, but occurred in very 

 variable number and association. A further accurate research on living and well- 

 preserved specimens is required to make out their mutual relations and signification. 



Ontogeny. — The development of the Auronectse is quite unknown, but will probably 

 offer interesting and valuable facts which explain the natural affinities of this interesting 

 order. Among the few spirit specimens of Stephalia corona which I discovered in the 

 collection of the "Triton" Expedition (1882), kindly forwarded by Dr. John Murray, 

 two specimens exhibited gonodendra (PI. VII. figs. 48, 49), whilst a third specimen 

 possessed no trace of them (PI. VII. figs. 39, 40). A very small medusome, found in the 

 same bottle (PI. VII. fig. 50), is probably a young larva of this Stephalia. This medusome 

 is composed of a pneumatophore (pa), an aurophore (I), a siphon (s), and a simple tentacle 

 (td). Unfortunately this larva (Anronula) was not well preserved, which prevented 

 further accurate examination. 



Synopsis of the Families of Auronectse. 



Trunk of the siphosome with a permanent central canal and a distinct primary mouth. 



Tentacles simple, without tentilla, . . . . . . .18. Stephalidae. 



Trunk of the siphosome without permanent central canal and distinct primary mouth. 



Tentacles branched, with a series of tentilla, . . . . . .19. Rhodalidse. 



Family XVIII. Stephalidae, Haeckel, 1888. 



Stephalidx, Hkl, System der Siphonophoren, p. 43. 



Definition. — Auronectse with a permanent central canal in the axis of the bulbous 

 trunk, opening at the basal pole by the permanent primary mouth. Tentacles simple, 

 filiform, without lateral branches. 



The family Stephalidae comprises the smaller and inferior forms of Auronectse, with 

 simple tentacles and a central permanent protosiphon, opening on the basal pole of the 

 vertical axis by a permanent primary mouth. I was able to examine accurately only 

 two genera and species of this interesting family, Stephalia corona (PI. VII.) and 

 Stephonalia bathyphysa (PI. VI.). 



The general composition of the corm, the structure of the nectosome and the 

 siphosome, and the form of the single organs composing them, have been described above 

 (p. 281). It is only necessary to add here the remark, that the Stephalidse, regarded from 



