126 THE NATURE AND VARIETIES OF 



The gamomorphic gemmae, in the case of the hood-eyed 

 Medusse again, are detached from their polyp stock as a 

 strobila or pile of zooids, by a successive transverse nssuring 

 of the body of the polype just below the tentacles. When 

 the segmentation is completed, there is developed round the 

 remaining portion of the body, immediately below the pile 

 of medusoids, a new circle of tentacles, so that when the 

 whole are thrown off the polype is enabled to resume its 

 pristine form and mode of life.* 



Such variations as have just been noticed, though per- 

 plexing to the systematic zoologist, are especially valuable 

 to the physiologist, as indicating the true relations of the 

 forms which occur in dimorphous species ; and I think they 

 are sufficient fully to bear us out in the conclusion, that 

 both the bare-eyed and the hood-eyed Medusse are to be 

 considered as gamomorphic zooids, and the polype-stock 

 from which they spring, as the typical form in each case. 

 In the one the orthomorphic form is, as usual, the most 

 conspicuous phase of the species, while in the other it is 

 quite eclipsed by the resulting gamomorphic zooid, which 

 is really a part of itself a detached and overgrown organ 



gonophore is considered by Prof. Allman to represent the concrete cells 

 of the polypes of such a ramuscule. (Edin. Philos. Journal, VII., 294, 

 IX., 111.) Mr. Huxley professes to adopt the term " gonophore" from 

 Dr. Allman, but the two authors do not appear to use the word in the 

 same sense. The latter applies it to the horny vesicle or urn which con- 

 tains one or more sporosacs or medusae, and speaks consequently of me- 

 dusiferous gonophores ; the other applies it to the medusoid itself, and 

 speaks of medusiform gonophores. 



* According to Desor, the strobila or pile of nascent medusoids is 

 formed inside the oral circle of tentacles; at the expense of the probos- 

 cidiform mouth, while the figures and description of Dalzell and Reid 

 represent it as external, the original tentacles being elevated on its sum- 

 mit, and a new one formed on the residuary base, when the whole pile 

 has been detached. Does this indicate a specific difference, as suggested 

 by Dr. A. Thomson in the Cyclop, of Anat. and Physiol. (Art. ovum 

 p. 22) ? 



