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



the cormidia of Abyla penfagona, detached from the common stem, live independently 

 and develop into a sexual Eudoxia. 1 Leuckart, who had made the same observation 

 simultaneously, demonstrated further that the monogastric Eudoxia campanula is 

 nothing more than the detached cormidium of the polygastric Diphyes acuminata 

 (5, pp. 41, 69 ; 8, pp. 268, 277). 



Huxley, in his excellent description of Diphyidse, separated the monogastric forms or 

 Eudoxias under the title " Diphyozooids." 2 He pointed out, with full reason, that it is 

 necessary on practical grounds to retain generic and specific names for the single 

 Diphyozooids, though they may possibly be only detached and independent portions of 

 " Polygastric Diphyidse." He gave a full anatomical description of many new or imper- 

 fectly known Eudoxise, and comparing their structure with that of the sessile cormidia of 

 corresponding polygastric Diphyidse, he suspected an ontogenetic connection between 

 these two forms (op. cit., 1859). 



During my residence in the Canary Island, Lanzerote (in the winter of 1866-67), I 

 had occasion to examine nearly all the interesting genera of Diphyozooids which Huxley 

 had accurately described. I was able to confirm most of his suppositions concerning 

 their connection with certain polygastric Diphyidse, observing directly the development 

 and detachment of the former from the latter (compare above, pp. 101, 102). 



The metagenesis which connects the monogastric and polygastric Diphyidse is 

 usually combined with a peculiar metamorphosis, some interesting cases of which have 

 recently been described by Chun (86-88). 



The detached and independent cormidia of Calyconectse — of the " Diphyozooids " — 

 arise in two different main-forms, Eudoxia and Erssea, which we regard here as repre- 

 senting two different families, Eudoxidse and Ersaeidas. Each Eudoxia is composed of 

 two medusoid persons, a sterile medusome (bract with siphon and tentacle) and a fertile 

 medusome (gonophore). Erssea differs from Eudoxia in the possession of a sterile " special 

 nectophore," and is therefore composed of three medusomes. 



The sterile medusome has in all Eudoxidse the same characteristic composition of three 

 essential parts — a bract (covering scale or hydrophyllium), a siphon placed in the dorsal 

 part of the bracteal cavity, and a tentacle attached to the base of the siphon. The fertile 

 medusome, or the gonophore, occupies the ventral part of the bracteal cavity. 



Bract or Hydrophyllium. — The protectum or bract of each Eudoxia ("Deckstiick or 

 Deckblatt " of German authors) is the modified umbrella of the sterile medusome. This 

 is very obvious in the genera Eudoxella (PL XXXII.) and Aglaisma (PI. XL.), where the 

 four radial canals of the subumbrella are preserved by heredity, whilst its muscle-plate is 

 lost by adaptation ; furthermore, the jelly cap is strongly developed, forming a thick and 

 firm protecting shield or cap (" covering scale "). 



Regarding the characteristic form of the bract, I distinguish two subfamilies among 



1 4, p. 78 ; 7, p. 205, Taf. xvi. figs. 1, 2. - 9, pp. 57-66, pis. iii.-v. 



