352 MR. A. DENDY ON WEST-INDIAN CIIALININE SPONGES. 



Hyatt's work on the North-American Poriferae already referred to ; he says, " two 

 specimens, pi. xv. figs. 22, 23, were introduced into the plates under the impression 

 that they were species of Spongelia, but the microscopical examination of the skeleton 

 shewed them to he spicular. Subsequently I found a specimen identical in every 

 respect with fig. 22, which, however, had fibres free from spicules, and a new exami- 

 nation of the originals of figures 22, 23 was made, disclosing the fact that the perfect 

 imitation of Chalina presented in my first preparation was accidental. This in its turn 

 led me to make renewed researches among the species of Tuha, and I now begin to 

 think that I may be obliged to withdraw from the position taken in the firi?t part of 

 this paper, and admit Tuha as a genus of Sponginee. It is very remarkable that there 

 should be any doubt on such a point ; but although I have examined more than fifty 

 microscopical sections of different species of Tula, sometimes several preparations to a 

 species, I cannot make up my mind as yet whether the spicules are indigenous or 

 foreign." 



I do not think that there can be much doubt that tlie spicules observed by Professor 

 Hyatt are to be regarded as " indigenous," and that tlieir presence in some cases and 

 absence in others is to be explained in accordance with the view enunciated above. 



The immediate cause of the disappearance of the spicules appears to be the develop- 

 ment of the spongin to such an extent as to form by itself a sufficiently strong skeleton. 

 In such a skeleton spicules would probably be not only useless but actually harmful, in 

 that they would tend to make the fibre rigid and brittle when it is desirable that it 

 should be elastic and flexible, in order to facilitate the free contraction and expansion 

 of the various parts of the canal-system, and in order to withstand the action of the 

 waves and currents in the shallow water in which horny-fibred sponges occur. 



Spongin appears to develop to a large extent only in warm climates and in tolerably 

 shallow water i, and under such conditions sponges with a strongly developed horny 

 skeleton are abundant. This general law is well illustrated by the present collection, 

 and also by the sponge fauna of the Eastern Mediterranean and of the Australian 

 area ^. 



Concerning the minute anatomy of the Chalininae I am, unfortunately, not able to 

 give any details in this place, as all the material at my disposal was dry. I have, 

 however, in another paper, given an account of the minute anatomy of a species of 

 PachychaUna ^, and Dr. K. von Lendenfeld deals with the subject in the forthcoming 

 paper already referred to. 



' Of. Hyatt, ' Revision of the North-American Poriferaa,' Part 2, p. 490 ; and Ridley and Dendy, Report 

 on the Monaxonida collected by H.M.S. ' Challenger,' p. Iv. 



" The Keratosa and Chalininje of the Australian area are being worked out by Dr. R. von Lendenfeld, who 

 has most kindly forwarded to me a proof of the first part of liis paper on the latter group. 



^ Proceedings of the Zoological Society of London, 1887, p. 524. 



