168 Dr. C. Chun on the Siphonophora. 



passive locomotion at the surface of the sea, that they cannot 

 compress their chambered air-sac. It is conceivable that, the 

 exertion of any active locomotion being impossible, both male 

 and female sexual animals are set free in the form of small 

 medusa?, namely Chrysomitrce. 



To summanze briefly, in conclusion, our judgment as to 

 the cyclical process of development of the Siphonophora, I 

 do not hesitate to assert that it shows a close relation to the 

 locomotion. Where numerous energetically acting necto- 

 calyces occur, as among the Polyphyidse (Hippopodius) and 

 Physophoridaa, the sexual animals remain sessile and often 

 degenerate into medusoid gemmae. - Where only one (Mono- 

 phyidse) or two nectocalyces (Diphyidse) produce a compara- 

 tively feeble locomotion, the diffusion of the species is pro- 

 vided for by the remarkable process of Eudoxia-foYmaitioii. 

 Nay, it may happen, as I have shown in the case of Mono- 

 phyes primordialis , that the first nectocalyx is replaced by a 

 second heteromorphous one, which is better fitted to carry 

 along the long trailing stem with the Eudoxia- clusters. From 

 the primitive organization of this Monophyes the life-history 

 of the species therefore appears to be spread over three gene- 

 rations, proceeding one from the other. Lastly, if, as in the 

 most highly organized Siphonophora the Pneumatophoridse 

 and Discoidese, the locomotive organs are wanting and loco- 

 motion takes place only passively, the diffusion of the species 

 is rendered possible by the sexual animals being rendered 

 motile. There is an alternation of generations that intervenes, 

 as an element of polymorphism, in the course of develop- 

 ment of the Siphonophora, and indeed of their highest repre- 

 sentatives, in this fashion, that on a polymorphic nurse gene- 

 ration anthomedusse are produced by gemmation, either 

 females alone (Pneumatophoridse), or males and females 

 (Discoidese), which only attain sexual maturity after their 

 separation. 



EXPLANATION OF PLATE V. 



General Indications :—g.sch. 9 genital nectocalyx; v, velum j s } fluid- 

 receptacle; m, stomachal sacj^/, tentacle; st 9 stem; d 9 bract; ^ecto- 

 derm ; en 9 endoderm. 



Cyclical development of Monophyes primordialis. 



Fig. 1. First generation : Monophyes primordialis, Chun, X 45. x, bud 



of the Muggitea-c&lyx ; jl, wing-like gelatinous ridges. 



Fig. 2. Second generation : Muggicea Kochii 9 Will & Busch, x 45. K, 



edges of the calyx. On the last group of individuals the rudi- 

 ment of the reserve genital calyx is already visible (#). 



Fig. 3. Third generation : Eudoxia Eschscholtzii, Busch, $ , X 45. The 



large genital nectocalyx (g.sch. l) had evacuated the ova from 



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