﻿April, 1857.] 



ELLIOTT SOCIETY. 



115 



our distinction questionable. But it appears pretty clear that the 

 outer covering of the bud at the stage when this takes place, is the 

 same that protected it before the tubes appeared, and if it were 

 not the §ame as the external surface of the future medusa's disk, 

 we should certainly observe at some point in the course of growth 

 a casting or shedding of this original covering. Now nothing of 

 this kind has ever occurred in the course of my own observations, 

 nor been mentioned by any observer with whose writings I am ac- 

 acquainted. The growth of the tubes, however, appear to be accom- 

 plished in the same centrifugal manner in both groups, with this 

 difference, that in the Campanularians they grow out synchronously 

 with the outgrowing disk, while in the Tubularians they are hol- 

 lowed out in the disk after the digestive trunk is already covered 

 by it. 



There are still two groups among Hydroid Medusae whose re- 

 lations to these two we ought to determine as far as practicable. 

 They are Siphonophorse and the Aeginidee, as well as the typical 

 fresh water Hydra. 



All the Siphonophorse appear to be developed after the manner 

 of the Tubularina, in free grape-like bunches as in Tubularia, (e. g. 

 Physalia, Physophora, &c.) or as in Clava and Coryne (e. g. 

 Porpita and Velella.) Huxley describes (Miiller's Archives 

 1851) the development of Diphyes, and from his description and 

 figures it is evident that the development of the bud proceeds ac- 

 cording to the Tubularian method. The observations of Quatre- 

 fages on the structure of Physalia (Annales des Sciences Natur- 

 elles 4 ieme, Ser. vol. II. p. 128 and PI. 4. 2) show pretty clearly, I 

 think, that the development of the tubes in the sexual Medusa fol- 

 lows the Tubularian plan and that the disk covers the digestive 

 trunk from the first. Also Kolliker has described in Jlgalmopsis 

 punctata the growth of the swim-bells, and these, according to his 

 description, have the disk closed in the earlier periods of existence, 

 even until the tubes are formed, and the interior of the bell entirely 

 without communication with the surrounding medium which it 

 last gains by formation of an opening, in some manner not ob- 

 served. This fact is specially to be remarked since here there is 

 no digestive trunk nor sexual organ. The figures given by Kolliker 

 (Schwimmpolypen von Messina) have all so general and striking a 

 resemblance to the various appearances of the Medusa buds at 

 various stages in Tubularia and Coryne, that I think it will at once 

 be recognized. On the other hand the free Medusa of Velella is 



