NOTES AND OBSERVATIONS ON BOARD H.M.S. RATTLESNAKE 83 



the former is yellowish white, the latter is deep red, and that the 

 stellate bodies, scanty in the former, are very numerous in the latter. 



However, pale specimens were frequent among the deep red 

 ones — without any other apparent difference — and the presence of 

 more or fewer stellate bodies is a mere question of degree. 



MM. Edwards and Audouin describe currents traversing the 

 " oscules " of the Tethya similar to those of a sponge. I did not 

 observe any currents, but I do not doubt their existence. 



Dr. Johnston says {op. cit. p. 82), " The propagation of Tethya is 

 by means of sporules or gemmules generated within the sarcoid 

 matter. The latter resemble the parent sponge in miniature, but 

 they have no distinct rind or nucleus, being composed of simple 

 spicula woven together by albuminous matter." 



I did not observe such " sporules or gemmules " in any of the 

 specimens I examined, but it can hardly be doubted that these bodies 

 are merely further developments of the " ova " which I observed ; and 

 as I found spermatozoa, it will follow, that the Tethyce are reproduced 

 by a process of true sexual generation. 



It would be most interesting to ascertain whether the "gemmules " 

 of sponge take their origin in a similar way, and whether true sper- 

 matozoa are developed here also. 



The specimens of Tethya observed presented several prominent 

 tubercles upon their surface, perforated by irregular apertures, from 

 which a liquid exuded when the animal was taken out of the water. 



When there was only one or two of these tubercles, the external 

 resemblance to some forms of Cynthia was very great. 



On cutting across one of these bodies, it was seen to be solid, and 

 •composed of three distinct substances ; viz. a central whitish spherical 

 mass, a deep red cortical substance, and between these two, forming 

 the largest part of the body, a yellowish red intermediate substance, 

 sharply separated from both the central and cortical substances. 



The two latter were united by radii of a silvery whitish colour, 

 which ran through the intermediate yellow mass, and became lost in 

 the cortical portion. 



Small canals took their rise at the apertures already mentioned, 

 and penetrating the cortical substance, ramified irregularly through 

 the intermediate substance, reaching as far as, but not penetrating, 

 the central substance. They appeared to be lined by a very delicate 

 smooth membrane. 



The general structure of the central, cortical, and intermediate 

 portions agreed pretty closely with the description already given 

 hy Johnston. 



G 2 



