142 Prof. AUman on the Hydroid Zoophytes. 



of the gonophore, arc seeu to be deeply bell-shaped. They are 

 remarkable for their large size, measuring in their transverse 

 diameter about 0*06", and a little more in their vertical diameter. 

 The manubrium extends to about the middle of the umbrella; 

 and the mouth is destitute of tentacles or lobes. There are four 

 radiating canals — each continuous, at the point where it intersects 

 the circular canal, with a very extensile marginal tentacle. The 

 tentacles are four in number, and originate in a large bulb con- 

 taining carmine-coloured granules, while a dark-reddish-brown 

 ocellus is superficially imbedded in a thickened portion of the 

 ectoderm on the outer side of the bulb. 



The bulbous base of the tentacle consists of a dilatation of 

 the tubular system of the Medusa at the point where the radi* 

 ating canals enter the circular, and having its endoderm greatly 

 thickened and lobed, and secreting coloured granules. The 

 ectoderm is here also much thickened on the inner side of the 

 base of the tentacle, so as to constitute a cushion-like lobe con- 

 taining imbedded thread-cells. 



In its extended state the tentacle is seen to have its thread- 

 cells grouped into very distinct knot-like clusters, which towards 

 the end of the tentacle are spherical, and so situated as to 

 appear to be strung upon the tentacle at intervals of about 

 three times the diameter of a cluster, but are less regular in 

 form, and more lateral and alternate in position near the base. 

 The terminal group of thread-cells forms a spherical bulb on 

 the tip of the tentacle, somewhat larger than any of the knot- 

 like groups along its length. 



There is no doubt of the complete continuity of the tube of 

 the tentacle, and coloured granules may be traced from the bulb 

 at the base to the very tip, though the peculiar arrangement of 

 the cells of the endoderm near the base would easily give rise to 

 the belief that the tube was interrupted by transverse septa. 



There is a wide velum ; and lithocysts are entirely wanting. 



The peculiar motion of the corpuscles in the tubular system of 

 Medusse would naturally be referred to the action of vibratile 

 cilia lining the walls of the canals, though I believe that these 

 cilia have never yet become an object of direct observation. In 

 the present little Medusa, however, I have distinctly seen them 

 in the radiating canals near the spot where these vessels enter 

 the circular canal, and again in the upper part of the canals near 

 their origin in the stomach. 



It will be at once apparent that the Medusa of C, eximia 



closely resembles that already described by Dujardin under the 



generic name of Sthenyo, as proceeding from a Coryne which he 



calls Synco7'yne decipiens^\ Indeed, though the Syncoryne 



* Ann. Sc, Nat. 1845. 



