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



Gonodendra. — The corm is monoecious and monoclinic, and bears numerous gono- 

 phores of both sexes, densely crowded beyond the corona of palpons, and forming an 

 inner corona around the base of the siphon. At the first glance I supposed that this 

 corona was composed of two large gonodendra only, a male and a female. A closer 

 examination, however, of the well-preserved spirit specimen, informed me that it was 

 composed of eight small gonodendra, four males (fig. 3, h) and four females (fig. 3, /) 

 alternating. The umbrella is well developed in both sexes, with four radial canals and a 

 ring-canal. Each gynophore contains a single large ovum, each androphore a club- 

 shaped spermarium with a central spadix. 



Family XL Athoeid^, Haeckel, 1888. 



Athoridx, Hkl., System der Siphonophoren, p. 38. 



Definition. — Physonectse monogastricae without nectophores, with a corona of 

 bracts which surrounds the pneumatophore, and a corona of palpons which surrounds 

 the base of the single siphon and the single tentacle. Pneumatophore without radial 

 pouches. 



The family Athorida? comprises some small, hitherto undescribed Physonectae, which 

 are in general similar to Athorybia or Anthophysa, but differ essentially from them in 

 the possession of only a single siphon. They agree with these Anthophysidaa (Family 

 XVII.) in the absence of nectophores, which are replaced by a corona of bracts. On the 

 other hand, they are similar to those well known Athorula-larvse, or " Athorybia-like 

 larvse," which are develojied from the fertilised egg of certain Physonectae, especially 

 Agalmkke. Compare Vogt (6, pi. x. figs. 32-37), Gegenbaur (7, Taf. xvii. fig. 11), 

 Claus (35, p. 557, Taf. xlviii.), Haeckel (84, Tafs. vii., viii., ix., fig. 60), Metschnikoff 

 (85, Tafs. ix., xi.), Fewkes (89, pi. iv.). 



The resemblance of the monogastric Athoridaa to these larvae of polygastric Agalmidae, 

 and the morphological likeness of their structure, make it probable that the former are 

 either remnants of the ancestral forms of the latter, or that they are larval forms which 

 under certain conditions sometimes attain sexual maturity (Psedogenesis). A further 

 accurate examination of these interesting small Physonects, and a complete knowledge of 

 their anatomy as well as ontogeny are required to recognise their relations to the other 

 families of this order. 



Two different forms of Athoridae were observed by me in 1881 during my residence 

 in Ceylon. The first and larger, Athoralia coronula, was very similar to a small young 

 Athorybia (Pis. XL, XII.); it will be described on another occasion. The second and 

 smaller form is described in the sequel as Athoria larvalis (PL XXI. figs. 5-8); it 

 differs from the former in the possession of a small rudimentary nectosac at the distal 



