472 



Prof. Allman on the Hydroida. 



tive sacs upon the radiating canals ; and I pointed out that the 

 structure of these sacs was identical with that of the gonosacs of 

 Clava, Hydractinia, &c, thus showing that they are definite 

 zooids produced by a process of budding from the gastrovascular 

 system of a properly non-sexual Medusa*. 



This view I endeavoured further to develope in a subsequent 

 paper f, when I designated such non-sexual Medusae by the 

 name of " gonoblastocheme," showing that they must be care- 

 fully distinguished from the proper sexual Medusa such as we 

 meet with in Sarsia, Oceania, Bougainvillia, &c, and for which 

 I proposed the name of " gonocheme." 



Now, I believe that the flat leaflike pouches in Geryonia are 

 entirely homologous with the more prominent generative sacs of 

 Obelia ; and if so, Geryonia must be viewed not as a gonocheme 

 or sexual Medusa, but as a gonoblastocheme or non-sexual 

 Medusa. The nature of the ova- and spermatozoa-producing 

 bodies in Cunina is more doubtful ; but still I can scarcely hesi- 

 tate to regard the generative elements as here also produced in 

 true gonosacs of essentially the same form as in Geryonia. The 

 doctrine of the gonoblastocheme will thus at once give us the 

 key to the explanation of the apparently anomalous phenomena 

 discovered by Haeckel, and will enable us to express them in the 

 following form, where Gon represents the gonosac. 



G + Gon 

 + 



+ 

 Gon 



-0- 



G+Gon| 



+ 



M 



+ 

 Gon 



..&c. 



© 



G+Gon| 

 + 



+ 

 Gon 



G + Gon 



+ 



+ 

 Gon 



&c. 



© 



G + Gon 



+ 



+ 

 Gon 



© 



G + Gonl@.-&c. 



+ 

 M 



+ 

 Gon 



© 



&c. 



&c. 



© 



&c. 



&c. 



* Leuckart had already recognized the zooidal nature of the generative 

 sacs in Aglaura (Wieg. Arch. 1856), and T. S. Wright had expressed an 

 opinion that in every gymnophthalmic Medusa all parts which are borne 

 by the umbrella — manubrium, tentacles, and generative sacs — must be 

 regarded in the light of buds. (Proc. Roy. Phys. Soc. Edin. 1856-570 



t Report on the Hydroida, Brit. Assoc. Rep. 1 863. 



