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 Calyconectse was made by the 

 excellent descriptions of different Diphyidse 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 Diphyidse; 

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

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

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

 detached Eudoxia} 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 Dvphyes acuminata (5, pp. 41, 69). 



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

 venient term Calycophoridse, and united in this family the true Diphyidse (with two 

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

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

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



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

 opposed it to all other Siphonophorse or Physophoridse. He gave the first exact descrip- 

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

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

 nectophore, under the name Sphseronectes kbllikeri, and rightly regarded it as the type 

 of a new family, Sphseronectidse. 3 Fifteen years later a very similar species of the same 

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

 observed its metagenesis and connection with that Eudoxia which Gegenbaur had 

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

 Calycophoridse, the Sphseronectidaa of Huxley, was called by Claus Monophyidse, in opposi- 

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

 Monophyida3 for all those polygastric Calyconectse which possess only a single permanent 

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

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

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

 named Polyphyidse by Chun (86, p. 12). L 



The Polyphyidse differ from the other Calycophoridse in the lack of bracts. A new 

 group, described in the secpiel as Desmophyidse, is intermediate between the Diphyidse 

 and Polyphyidse, 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. 106. - 9, pp. 29, 50, pi. iii. fig. 4. 



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



