64 



HTDROZOA. 



Gemmation of Medusoids : — a, Biplonema Islandica, showing 

 young Medusoids budding from the tentacles; b, Sarsiagemmifera, 

 vith Medusoids arising from the sides of the polypite; c, Sarsia 

 proUfira, in which Medusoids are seen to sprout from the junc- 

 tion of the tentacles with the marginal canal. (All magnified.) 



L UCERNABIDJE. Still more singular phenomena 

 appear in the life-history of LucernaridcB. In 

 Aurelia, Gyanea, and Chrysaora, the ova originate 

 mthin the generative cavities of the gigantic repro- 

 ductive bodies previously described. Thence they 

 are transferred, in some unknowTi manner, to the 

 peculiar pouches formed along the margins of the 

 dependent lips of the polypite, and on their way 

 to these pouches are, in all probability, fertilised by 

 contact with the diffused spermatozoa. Segmenta- 

 tion of the vitellus, and other primordial changes, 

 are undergone by the young ovum while yet 

 within the pouch, from which, about the close of 

 the thii'd day, it comes forth, to enjoy, for a brief 

 period, an active, free-smmming existence. At 

 first it appears as an oblong, flattened, ciliated 

 body, or ' planula,' of very minute size, composed 



