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



published up to his time ; but he could not distinguish the natural groups critically. 

 Marked progress in our anatomical knowledge of the Calyconectae was made by the 

 excellent descriptions of different Diphyidae which were published in the third period of 

 our knowledge of Siphonophorse (from 1853 to 1859, 4-10) by Kolliker, Leuckart, Vogt, 

 Gegenbaur, and Huxley. Two of these celebrated zoologists simultaneously and inde- 

 pendently discovered, in the spring of the year 1853, that the monogastric Diphyidae, 

 or the so-called Eudoxise, were the isolated individual groups (or cormidia) of the 

 polygastric Diphyidae, detached from the common stem, and that the former were 

 connected with the latter by a regular metagenesis. Gegenbaur observed in Messina the 

 detached Eudoxise of Abyla pentagona. 1 The same observation was made at the same 

 time in Nice by Leuckart, who further demonstrated that the monogastric Eudoxia 

 campanula was the detached sexual zooid of his Diphyes acuminata (5, pp. 41, 69). 



Leuckart in the next year (8, p. 256) replaced the name Diphyidae by the more con- 

 venient term Calycophoridae, and united in this family the true Diphyidae (with two 

 nectophores, loc. cit., p. 257) and the Hippopodidae (with a biserial nectosome, composed 

 of four or more nectophores, loc. cit., p. 298). The latter were formerly regarded as a 

 separate family of Physophoridae, though they possess no float filled by air. 



Huxley in his great work (9, 1859) adopted the main group Calycophoridae, and 

 opposed it to all other Siphonophorae or Physophoridae. He gave the first exact descrip- 

 tion of many hitherto incompletely known forms, mainly Abylidae. He was also the first 

 to describe a very remarkable Calycophoridj which possesses only a single permanent 

 nectophore, under the name Sphieronectes kollikeri, and rightly regarded it as the type 

 of a new family, Sphaeronectidae. 2 Fifteen years later a very similar species of the same 

 genus was described by Claus under the name Monoplxyes gracilis (70, pi. iv.). He 

 observed its metagenesis and connection with that Eudoxia which Gegenbaur had 

 described in 1854 as Diplophysa inermis. 3 The peculiar family represented by these 

 Calycophoridae, the Sphaeronectidae of Huxley, was called by Claus Monophyidae, in opposi- 

 tion to Diphyidae. Following the systematic manuals of recent years, I adopt the term 

 Monophyidae for all those polygastric Calyconectae which possess only a single permanent 

 nectophore, while I restrict the term Diphyidae to those forms which have two permanent 

 nectophores. A third family is formed by the Hippopodidae, 4 which possess numerous 

 (at least three or four) nectophores arranged in a biserial nectosome ; they were afterwards 

 named Polyphyidae by Chun (86, p. 12). 



The Polyphyidae differ from the other Calycophoridae in the lack of bracts. A new 

 group, described in the secpael as Desmophyidae, is intermediate between the Diphyidae 

 and Polyphyidae, having in common with the former the possession of a bract on each 

 eudoxome, with the latter a biserial nectosome, composed of numerous nectophores. 



1 7, p. 295 ; 4, p. 78 ; 31, p. lot!. " 9, pp. 29, 50, pi. iii. fig. 4. 



3 7, Taf. xvi. fig. 3. * Kolliker, 4. p. 28. 



