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



Blainville, in his Actiuologie (24, pp. 125-140), and Lesson, in his Acalephes (3, 

 pp. 425-465), collected the scattered descriptions and figures of the older observers, and 

 distinguished a greater number of genera, but without any clear anatomical under- 

 standing and without critical judgement. 



The excellent naturalists, who, in the sixth decade of our century (1853 to 1859), 

 did so much for the anatomical knowledge of Siphonophorse, gave also the first accurate 

 description of the typical Diphyidae, mainly Diphyes and Abyla (4-10). Kolliker 

 (4, Tab. ix.-xi.) gave an excellent description of three Mediterranean types — Praya 

 diphyes, Diphyes sieboldii, and Abyla pentagona. Vogt (6, Tab. xvi.-xxi.) gave 

 beautiful drawings of the same forms, and also of Galeolaria aurantiaca. But the 

 greatest progress in the knowledge of Diphyidae, mainly regarding their development 

 and connection with Eudoxidse, was made by Gegenbaur (7 and 10) and by Leuckart 

 (5 and 8). The former described, too, a greater number of new species (of Praya, 

 Dip>hyes, and Abyla, 10). 



The most complete anatomical and systematic description of the polygastric 

 Diphyidae, and of their offspring, the monogastric Eudoxidse, as also the best and 

 fullest account of the whole family up to our days, was given in 1859 by Huxley 

 (9, pp. 30-66, pis. i.-v.). He restricted the family Diphyidae to the genera Diphyes and 

 Abyla in the sense of Eschscholtz, and separated them from Praya, as the type of 

 another family, Prayidse (Kolliker, 4, p. 33). He gave, further, the first accurate descrip- 

 tion of numerous Diphyozooids (or Eudoxidse), of seven different genera, and indicated 

 probable ontogenetic connection with different forms of Diphyes and Abyla. 



During my residence in the Canary Islands, from December 1866 to February 1867, 

 I had the opportunity of examining typical representatives of all the eight genera of 

 true polygastric Diphyidae which are described in the sequel, and there I drew from 

 nature the figures, which will be seen in Pis. XXXI. to XLII. of this Report. The 

 greater number of the Diphyidse, there observed by me, were afterwards found again in 

 the collection of the Challenger, mainly in bottles containing surface animals, which were 

 taken in the Tropical and Subtropical Atlantic (Stations 334 to 354; March 14 to 

 May 7, 1876). In Lanzerote I observed directly the metagenesis of Diphyes (with 

 Cucullus), Diphyopsis (with Erssea), Abyla (with Amphiroa), Bassia (with Spihenoides), 

 and Calpe (with Aglaisma). 



Nectophores. — The two nectocalyces, which, in all Diphyidse, are placed at the top of 

 the stem, appear in three different stages of phylogenetic development, and these deter- 

 mine the division of the family into three divergent subfamilies. The first subfamily, 

 Prayidse, has two nectophores of nearly equal size and similar form, opposed to one 

 another ; sometimes the first is somewhat smaller than the second ; their surface is 

 rounded, the jelly-substance very soft. Their shape is either mitriform or reniform 

 (Praya, PI. XXXI.), or more hemispherical (Lilyopsis). 



