No. 7. — Contributions to a Knowledge of the Tubular Jelly-fishes. 



By J. Walter Fewkes. 



I. The Development of the Tentacular Knob of Physophora 



hydrostatica. 



The anatomy of those animals known to the zoologist as the Sipho- 

 nophorse, or tubular Jelly-fishes, has been carefully studied, and minutely 

 described. I present certain points in which my observations or conclu- 

 sions differ from those of other naturalists. I have also discussed at 

 length the limits and synonymy of the genus Halistemma^ since I think 

 it embraces animals with generic differences, and I conclude with a brief 

 mention of North American Siphonophorae and Velellidse, adding three 

 genera to those already described for our coasts. The development of 

 the structures which have received the name of tentacular knobs has a 

 certain interest, particularly the different stages in growth of that per- 

 haps most complicated of all, the knob of Physophora. The development 

 of these structures long since attracted attention, and Claus * twenty 

 years ago (1860) published a description, with figures, of the younger 

 stages of the knob in Physophora hydrostatica. Keferstein and Ehlers, 

 to whom science owes so many discoveries in regard to these Jelly-fishes, 

 followed this work with certain corrections and additions of the most 

 important character. Their investigations were made upon a species of 

 Physophora called P. Philippi, identical with or only distinguished from 

 P. hydrostatica by the possession of lateral appendages to the external 

 walls of the knob. The account which they give in most particulars 

 applies also to P. hydrostatica, which' has furnished me the material for 

 my studies of the developmental history of the tentacular knob in this 

 genus. 



The growth of the knob of Physophora, although quite simple, is more 

 complicated than that of any other Siphonophore. I have only, how- 

 ever, considered it necessary to figure a few stages assumed in this 

 growth, illustrating the peculiar asymmetrical form of the involucrum, 

 and the embryonic appendages to the sacculus, which are provisional in 



* Ueber Physophora hydrostatica nebst Bemerkungen liber andere Siphonophoren. 



VOL. VI. — NO. 7. 1 



