

v 



Dr. C. Chun on the Siphonophora. 165 



formed, as also in the Polyphyidee, by a great number of 

 nectocalyces, or in the only Physophorid in which the latter 

 are wanting, namely Athoryhia, by medusa-like natatory 

 movements of bracts. 



Are we to regard it as surprising that here, where provision 

 is made for the distribution of the species by means of nume- 

 rous energetically acting nectocalyces, the sexual animals 

 themselves remain immovably attached to the stem ? That 

 in the case of the Monophyidaj and Diphyid^e, with their 

 comparatively insignificant locomotion by means of one or 

 two nectocalyces, the acquisition of mobility by the sexual 

 animals furnishes an efficacious instrument for the distribu- 

 tion of the species can be seen at once. In the Polyphyidse 

 the male and female individuals still exhibit a medusiforra 

 development, but the umbrella appears reduced ; while in the 

 Physophorid ee, which are still furnished with numerous necto- 

 calyces, it represents merely a mantle-like envelope of the 

 single ovum. 



If, then, our notion is correct, that the separation of the 

 sexual individuals occurs as a compensation for an insufficient 

 power of locomotion and the resulting imperfect distribution 

 of the species, we have, in conclusion, still to inquire how the 

 other Siphonophora, which usually quite give up any active 

 locomotion, effect their diffusion. The Rhizophysidse and 

 Physalice have been frequently united with the Physophoridae, 

 Nevertheless they differ so much from the latter that I prefer 

 placing them as a distinct order, il Pneurnatophoridas," side 

 by side with the Calycophoridae and Physophorid^. Their 

 air-sac especially acquires an imposing magnitude, and com- 

 municates with the exterior by an opening. Locomotive 

 organs in the form of nectocalyces, or movable bracts, are 

 wanting ; and the characteristic/' hepatic bands " of the polyps 

 are broken up into numerous isolated villi. While Rhizophysa 

 is enabled to ascend and descend by compression of the air- 

 sac, the adult Physalia, with its enormous bladder occupying 

 nearly the whole stem, is driven about at the surface of the 

 sea as the sport of the winds and waves. 



As to their sexual relations, there still prevails a certain 

 obscurity ; and although I may be unable to dispel this com- 

 pletely, I believe I have advanced a step nearer to its solu- 

 tion. Huxley, as is well known, put forward the supposition 

 that in Physalia the medusiform buds, seated beside the nume- 

 rous male medusoid gemmae, might become developed into 

 female sexual animals and separate from the colony. I 

 doubted long as to the correctness of this hypothesis of Hux- 

 ley's ; but, after the examination of perfectly mature sexual 



