132 ^ BULLETIN OF THE 



III. The Tubes in the larger Nectocalyx of Abyla pentagona. 



The best description which I have found of the course of the chymif- 

 erous tubes o{ Abyla pentagona is by Gegenbaur.* At the regular meet- 

 ing of the Boston Society of Natural History, on Novembers, 1879, I 

 pointed out the existence in Abyla of a supplementary tube, which takes 

 an origin from the junction of one of the radial vessels with the circum- 

 velar tube, and extends diagonally across one quadrant of the bell, ending 

 in an enlargement of a peculiar kind. I also indicated the difficulties 

 which present themselves to a determination of an homology between 

 the chymiferous tubes in Abyla and other nectocalyx-bearing Siphono- 

 phores, on account of these supplementary tubes. The bilateral sym- 

 metry shown quite well in the swimming-bells of other Calycophoridse, as 

 Epibulia, Diphyes, and Praya, in the Hippopodidse, and in Agalma, Agal- 

 mopsis, Halistemma, Apolemia, and Physophora of the Physophoridse, 

 does not appear in the different spheromeres of Abyla. In all cases 

 except Abyla, bilateral symmetry, as referred to a plane passing through 

 two opposite chymiferous tubes of the bell, and the ventral line of the 

 stem, is very easy to make out. The want of symmetry in Abyla is the 

 result of a covering in of the " Langskanal " by a growth from one of the 

 bounding ridges of the bell. A like covering of the canal is to- be seen 

 in Monophyes, where the nectocalyx is hemispherical, with none of those 

 marked elevations and projecting points continued beyond the opening 

 of the bell which are so prominent in Abyla, and to which it owes both 

 of the specific names pentagona and trigona. I have noticed no varia- 

 tion from a normal arrangement of the chymiferous tubes in Monophyes, 

 (PI. III. fig. 6.) 



IV. On Halistemma, Agalma, and Agalmopsis. 



The adoption of the generic name Halistemma has now become almost 

 universal, and seems necessary for a proper understanding of the genera 

 of Siphonophores, about which there has existed considerable confu- 

 sion. The following animals have, I think, been erroneously placed in 

 this genus ; viz. Halistemma tergestinum, Glaus, and Halistemma carum, 

 Haeckel. Huxley, in "Oceanic Hydrozoa," proposed the name for cer- 

 tain forms of tubular Jelly-fishes, with elongated axes, biserial rows of 

 swimming-bells, and naked tentacular knobs with a single terminal fila- 

 ment. The genus Agalma, by his classification, was to include those the 



* Neue Beitrage zur Naheren Kenntiiiss der Siphonophoren. Nova Acta Carol., 

 Vol. XXVn., 1860, pp. 349 -.356. 



