﻿April, 1857.] 



ELLIOTT SOCIETY. 



169 



4th ghottp. SIPHONOPHORJE.* Eschscholtz. 



1 have already separated from Siphonophorae the Velellidse as 

 quite a distinct group, having a closer relation to the larval commu- 

 nities than the former, which it appears to me, from a careful con. 

 sideration of the facts within my knowledge, receive their most 

 natural explanation by a comparison with the budding Sarsias and 

 Lizziae. So far as I am acquainted with the literature of this subject, 

 there is nothing really known of the embryology of these Medusae. 

 We are only acquainted with their medusa-stages, and the polypoid 

 stage, in none of them, is known. To begin with what seems to 

 me the simplest case that of Eudoxia and Ersaea, we have 

 a modified medusa-disk as the base of the community, corres- 

 ponding to the bell of the budding Lizzia, its digestive trunk 

 (tubulus suctorius Esch.) corresponding to the same organ in 

 Lizzia, and from the walls of this, proceeding as in Lizzia, Me- 

 dusae, which here, however, instead of being all sexual, are of 

 three classes, one of which is confined to reproduction j another, 

 has no other organ than a swim-bell, pierced by circulatory 

 tubes, and restricted probably entirely to locomotive and respiratory 

 functions ; thirdly, there are growing from the walls of the digest- 

 ive trunk, tentaculiform organs. Now, if my supposition be cor- 

 rect, these latter cannot be the homologues of the tentacula of 

 the ordinary free Hydroid medusas, but must be medusa-buds 

 gradually modified into the form of tentacula, and if true here, 

 the same is true for the tentacula of all Siphonophorse. According 

 to my observation, the ascending canal of the basal medusa's 

 disk, in Eudoxia, contains air, (pi. 8, fig. 9, a,) and this is the homo- 

 logue of the air-bladder in all the other Siphonophorse, not ex. 

 eluding Physalia. The digestive trunk also of Eudoxia, appears 

 to me the true homologue of the main stem in such genera as 

 Physophora, and Agalmopsis, supporting the swim-bells and the 

 so-called polyps, bracts, and tentacula, as well as the sexual indi- 

 viduals, all which L consider special modifications of medusa-buds, 

 such as exist on the trunk of certain Lizzias and Sarsias. In 

 Physalia, this tubular modification of the trunk appears to be re- 

 duced to a rudiment. In Prayia, which is certainly not distantly 

 allied to Eudoxia, the basal medusa-disk and its cavity, as well as 



* In his " Lectures on Comparative Embryology," Boston, 1849, Professor Agassiz 

 already considers the Siphonophorse communities of individuals. 

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