282 Proceedings of the Royal Physical Society. 



had been kept a few days in fresh water) I have figured with 

 the camera in PL XII. fig. 12. Its resemblance to Carus's 

 figure of the Medusa, Cunina globosa (Esch.), which I have 

 copied in fig. 11, is very striking. 



As the Medusa is a multiplex organism, we must inquire 

 how far it is homologous with the generative sac of the Hy- 

 droid Zoophyte. 



Prof. Allman, in his paper on Cordyhphora (Phil. Trans, 

 vol. cxliii.), advanced the doctrine that the generative sac 

 was homologous with the whole Medusa — a doctrine based 

 upon an erroneous conception of the cavity in which the 

 generative elements are contained. In a "Note on Dioecious 

 Eeproduction in Zoophytes" (Edin. New Phil. Jour., vol. iv. 

 p. 88), I stated that " the reproductive buds [generative 

 sacs] (of Goryne) were filled with ova developed from the 

 exterior of a hollow central stalk, a diverticulum of the 

 alimentary canal;" and further, " The peduncle of the 

 Medusa-bud [or budded Medusa] appears to me to be homo- 

 logous with the entire reproductive capsule [generative sac] 

 of Coryne glandulosa, &c." This view is now adopted by 

 Prof. Allman, who writes, in " Annals of Natural History," 

 (vol. vi. ser. 3, p. 4), " The manubrium is the whole of the 

 1 peduncle,' ' stomach,' or by whatever other name it may be 

 called, which depends from the centre of the umbrella in a 

 Medusa or medusoid ; and I apply the same term to what 

 I consider the homologous part in a sporosac, namely, the 

 whole sporosac minus the ectotheca and mesotheca." Now, 

 the ' sporosac,' less the ' ectotheca' and ' mesotheca,' is the 

 simple generative sac, which, therefore, Prof. Allman has 

 agreed with me in considering homologous with the peduncle. 



But I would now very much modify the above view. We 

 must keep in mind that each of the eight elements of a 

 medusoid has three distinct functional subelements ; that 

 the single reproductive subelement of the Medusa exists, 

 as in Stomobrachium, uncombined ; that where the peduncle 

 is the reproductive organ of a free Medusa, as in Sarsia, it 

 consists of two subelements of different function combined, 

 each exercising its separate function, alimentative or repro- 

 ductive ; that an organ composed of a single subelement (a 



