229 



On the Natural History and Histology op Sponges. 

 By B. W. Priest. 



{Read January 28th^ 1881.) 



PLATES XVII, XVIII. 



It is only witliin the last few years that the Sponges or Porifera 

 have been classed in the animal kingdom, thanks to the modern 

 improvements of our microscopical appliances, which have enabled 

 us to work out their minute histological structure. They were long 

 thought to be of a vegetable nature, on account of some species, as 

 in our freshwater Spongilla for instance ; the green colouring matter 

 being due to the formation of chloroj^hyll, which, of course, is in- 

 fluenced in the same manner by the action of light as it is in plants, 

 and also by their being fixed to one place. 



With the exception of those that belong to the genus Spongilla 

 all known Sponges are marine, but they vary much in their habit of 

 growth, some being obtained only from great depths, others between 

 the tide marks, on weeds, stones, and the piers and piles of our 

 shores, some of which are mere films incrusting the substances on 

 which they grow. 



It appears, by reference to Dr. Johnston's work on the SpongiadcT, 

 that the first British Sponge recorded was in 1616 ; since that time 

 the species have been multiplied greatly, and would bear a deal of 

 cutting down, young specimens being in many cases taken for 

 different species ; but some excuse may be made, in that only a few 

 have studied this branch of Natural History. 



For our present purpose, perhaps, the late Dr. Boweibank's classi- 

 fication will be the best to adhere to, although every year, I may say 

 every month, brings something fresh to our knowledge that will 

 make it necessary to alter their arrangement at some future time. 

 The Sponges are divided into three orders : 

 The Calcareous, Siliceous, and Keratose. 



The Calcareous Sponges are few in comparison to the other two, 

 and include the well-known Grantias, whose histology perhaps is one 

 of the easiest to make out of the marine ones. 



Journ. Q. M. C, No. 47. t 



