23G B. W. r-RIEST ON THE NATURAL HISTORY 



of which may be met with in the '' Annals of Natural History," 

 vol. vi., p. 220, in a paper by Mr. Saville Kent, where he explains 

 their occurrence in a Sponge dredged up in the Noma expedition. 

 (Figs. 7 and 8. Plate XVII.) 



I have drawn roughly here, a copy of the figures given in the 

 Annals just mentioned, of one of these bodies, along with one of 

 Xanthidium ramosum, and I think you will agree that there is a 

 resemblance and some analogy between the two, although the fibres 

 of the former are somewhat finer than the tentacula of the Xanthi- 

 dium. Of course we have to find these bodies occurring in other 

 specimens of Sjoonges to corroborate the idea, and it would be a great 

 boon if the captains of vessels and others who go long sea voyages 

 would try and obtain specimens of Sponges, and distribute them 

 to different Societies, who have members interested in that branch 

 of natural history. In the first volume of the " Transactions of the 

 Eoyal Microscopical Society " there is an account of some living 

 Xanthidia having been sent over from America, found in some pool 

 or pond, but I think that went to negative the idea entirely of their 

 being Sporangia, as Desmids have never been found, that I am 

 aware, in salt or even brackish water, and therefore could not be 

 found in Flint. 



It has long been a disputed point what these bodies are, and 

 perhaps some of the members present could enlighten us a little 

 more on the subject. 



Perhaps a word or two on the examination of Sponges may prove 

 of interest to those who wish to follow up the study of this interest- 

 ing subject. 



Unfortunately the marine Sponges cannot be kept long alive in an 

 aquarium, therefore we have to content ourselves with examining 

 them the next best way. 



Those who would work out their minute histology, should, if 

 possible, obtain living specimens in as many stages of development 

 and growth, and whenever they chance to come across them, follow 

 out the ciliary action in the chambers and passages. 



A good and interesting way to see the currents in Grantia com- 

 pressa is to slit up the side of the Sponge with a fine pair of 

 scissors, laying it open in a cell with sea water, with the inner sur- 

 face upwards, and so arranged that a high power can be brought to 

 ])ojir on it — a few grains of indigo or carmine being placed in the 

 water. 



