166 Dr. C. Chun on the Siphonophora. 



clusters, for which I am indebted to my friend Von Petersen, 

 I must now thoroughly agree with him. These sexual clusters 

 are from a large Pliysalia which appeared in the Bay of 

 Naples after the spring storms of 1879. At the first glance 

 we detect in them a considerable number of medusae, which 

 attract attention by their size. By means of long peduncles 

 traversed by a canal they are attached among the gemmae 

 filled with nearly mature spermatozoa and the sexual tentacles 

 characteristic of Pliysalia. On closer examination a consi- 

 derable aperture, fringed with a velum, may be easily recog- 

 nized in the gelatinous umbrella, into the cavity of which it 

 leads. The cavity is lined with ectodermal cells, which in 

 young examples are arranged in projecting pads, in older 

 ones are evenly diffused, and at their base differentiate nume- 

 rous smooth muscular fibres running circularly. The vascular 



lamella surrounds the epithelial musculature of the sub- 

 umbrella, and shows in transverse section the lumina of four 

 vessels, which open within the velum into an annular canal. 

 An ectodermal fibrous cord, which runs at the base of the 

 velum, I am inclined to interpret as a nervous ring. On the 

 other hand, we cannot perceive either tentacular pads^, mar- 

 ginal bodies, or sexual organs. A stomachal peduncle, in the 

 wall of which the sexual organs will probably originate, is 

 indicated by a small elevation at the bottom of the cavity of 

 the umbrella. 



Now, if we take into consideration the considerable size of 

 these medusae (they measure 2 millim. in breadth, and 5 to 

 6 millim. in length with the peduncle), and their organiza- 

 tion, which is indicative of a free independent life, there can 

 hardly be any doubt that, after the development of a mouth- 

 aperture and of the tentacular pads, they separate and grow 

 up into female anthomedusae. Thus, again, in the Physalice, 

 which are destined to a passive mode of locomotion, the dis- 

 tribution of the species is secured by the acquisition of mobi- 

 lity by the female sexual animals. That the medusas are 

 really separated appears from the following observation : 



• • i 



In examining the sexual clusters we find now and then gela- 

 tinous stalks 3 millim. long, traversed by a vessel. They 

 perfectly resemble the basal pedunculiform section of the 

 medusa-buds, and are easily distinguished from the sexual 

 tentacles. As a matter of fact, a careful examination shows 

 that the medusas do not separate in their whole length, but that 

 their inferior pedunculiform half remains adherent to the 

 genital cluster. If we consider that the Physalics always live 

 together in crowds, and that from the enormous production of 

 spermatozoa the contact of these with the ova produced by the 





