



^v 



Dr. C. Chun on the Siphonophora. 167 



medusse is rendered easy, it need not surprise us if only the 

 female individuals lead a free existence. 



But what I have here communicated with regard to the 

 sexual relations of Physalice, may with the greatest probability 

 also be applied to those of Rhizophysa filiformis. Hitherto 

 certain small clusters of mulberry-like aspect, originating 

 isolatedly upon the stem, were described as the sexual organs 

 of the latter, although no sexual products had been detected 

 in them. I was therefore greatly interested when I was able, 

 in a specimen of Rhizophysa which made its appearance in 

 October, to demonstrate that these mulberry-like appendages 

 become developed into sexjial clusters, which might almost be 

 confounded with those of a young Physalia. Each of the 

 knob-like pads in the cluster begins to draw out into an elon- 

 gate oval form, appears diminished like a peduncle at its 

 base, and shows in about its middle the rudiment of a medusa- 

 bud. As is shown by still older sexual clusters, there are 

 produced at the periphery of the bud, which still more dis- 

 tinctly shows the form of a medusa, about six or eight ex- 

 crescences formed of ectoderm and endoderm, while the distal 

 extremity of the whole lateral branch is produced into a 

 sexual tentacle. The oldest genital clusters (those seated at 

 the lower end of the stem) consequently consist of a peduncle 

 abundantly furnished with muscular fibres and very contrac- 

 tile, the cavity of which communicates with that of the stem, 

 and on the other side extends into about twelve lateral 

 branches. Each of these lateral branches, with its appendages, 

 so completely resembles the corresponding parts of Physalia, 

 that I do not hesitate to regard the medusa-bud as the pro- 

 ducer of the ovum, and the knob-like buds as young seminal 

 capsules. The observation of still further advanced genital 

 organs will show whether, as seems to me very probable, the 

 female individuals also become free in the form of medusas in 



Rhyzophysa. 



I believe I have proved that Rhizophysa and 



Physalia show a close relationship, which justifies us in rais- 

 ing them into the order Pneumatophoridse. But what appears 

 to be of special interest in connexion with the question of the 

 origin of alternation of generations among the Siphonophora, 

 is the circumstance that with the cessation of active locomo- 

 tion (for the ascent and descent of the Rhizophysa can hardly 

 come under consideration for the distribution of the species in 

 a horizontal direction) the necessity again occurs of rendering 

 at least the female sexual organs motile in the form of antho- 

 medusas. If, finally, we glance at the highest Siphonophora, 

 namely the Velellidae, they appear so perfectly adapted to a 





