THE HYDROMEDUSAE 



47 



from observations on a few forms which are too widely different to 

 allow of a general developmental scheme being as yet laid down. 

 A planula is apparently always formed ; the first individual budded 

 from it may be a pneumatophore (Halistemma), nectocalyx 

 (Epibulia), or hydrophyllium (Agalma). The coenosarc may be 

 a lateral extension of the first gastrozooid (Cystonectae), or may 

 be its elongated stem (1 Physophoridae, Calyconectae). 



APPENDIX TO HYDROMEDUSAE. No. I. 



Limnocodium and Limnocnida. 



These are two freshwater medusae, the first-named known only from 

 the Victoria Regia Tank of the Royal Botanic Society in London, the 



52. Limnocodium, as seen floating, x 5. MR, marginal nerve and cnidoblast ring ; Ve, 

 velum ; 1'T, perradial tentacle. (After Lankester.) 



53. Polyps of Limnocudiiim on weed (after A. G. Bourne). 



54. Diagram of the sense organs of Limnocodium and Limnocnida. C, cavity of the 

 vesicle, which in Limnocodium is continued as a canal into the velum ; EC, ectoderm of the 

 sense organ ; EV, ectodermal lining of the vesicle ; EN, refringent endoderm cells of the sense 

 orpin ; Stf, granular endoderm cells of the sense organ ; EN", position of endoderm of the cir- 

 cular canal. (After Lankester and Giinther.) 



second known only from Lake Tanganyika. They undoubtedly belong to 

 the Hydromedusae, and to different orders of the class, but it is still a 

 matter of difficulty to assign them to any of the existing orders. 



Limnocnida (Fig. 55) presents points of resemblance both to Antho- 

 medusae and to Xarcomedusae. It shares the manubrial position of its 

 generative organs with both these orders ; but in the shortness of the 



