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connected with the Hydroid Polyp from which they arise. This anal- 

 ogy further sustains the view that Hydroid Polypi are true Medusae, 

 inasmuch as here we have a crown of medusoid structure resting upon 

 a stem similar to the stem of attachment of young Medusae, which is 

 only much more elongated, and from which similar branches may bud. 



The analogy of some genera of Hydroid Polypi, such as Coryne 

 and Syncoryna, to Medusae, is apparently more remote, from the cir- 

 cumstance that the tentacles are scattered around the surface of the 

 terminal bulb ; but it requires only a close comparison of the mode 

 of formation and increase of the tentacles in those genera in which 

 they form a regular whorl to satisfy the observer that even in those 

 Medusas in which the regular crown of tentacles seems to form 

 strictly a whorl, the tentacles in their successive development do not 

 arise from the same level, but that there are some which are inserted 

 nearer the centre of the axis than others ; so much so that an elonga- 

 tion of the axis upon which they stand would produce an arrangement 

 similar to that which we notice in Coryne and Syncoryna, where they 

 are regularly scattered. Even in the latter genus the analogy is 

 complete, for the uppermost end of the main bulb terminates with a 

 regular opening, surrounded with minute fringes, though this aperture 

 seems to have been overlooked by former observers. Though a 

 mouth is mentioned in the characteristics of Coryne, in Syncoryna it 

 seems to have escaped attention. I may add that there is a remark- 

 able correlation between the number of tentacles which exist nomi- 

 nally upon a terminal bulb of Syncoryna and the nominal number 

 of radiating tubes and tentacles which are developed in the little 

 Sarsia produced from that Hydroid Polyp. Syncoryna has generally 

 sixteen tentacles, four times as many as the free Medusae to which 

 it gives birth. 



In no Hydroid Polyp is the structure of the tentacles more closely 

 allied to that of some of the naked-eyed Medusae than in Syncoryna, 

 for their club-shaped tentacles, with lasso cells, remind us most 

 distinctly of the tentacles of Slabberia ; and, so far as these compa- 

 risons are conclusive, there remains no doubt in our mind that, from 

 their structure and Morphology, the so-called Hydroid Polypi must 

 be considered as true Medusae, among which they constitute a type 

 analogous to the stalked Crinoid among Echinoderms ; an analogy 

 which is the more remarkable, as in their ultimate generation Hydroid 

 Polypi produce free Medusae, while the Comatulae arise from the Cri- 

 noids provided with stems. 



