474 Mr. G. Bidder. [May 12, 



ing and protecting the younger foliar structures, from the time of 

 their first formation. 



V. "Note on Excretion in Sponges." By George Bidder. 

 Communicated by Adam Sedgwick, F.R.S. .Received April 

 9, 1892. 



In a review* of Mr. Dendy's work on the Homocoela, I briefly 

 described (p. 628) the "flask-shaped" or "glandular" epithelium, 

 which I believe to form the most common external covering in all 

 groups of sponges. On p. 631 are shortly mentioned certain other 

 granular cells, believed by Metschnikofi: to be mesodermal, and by 

 Dendy to be the dwelling place of symbiotic Algae ; I proposed the 

 neutral name of " Metschnikofi 1 cells." " In Ascetta clathrus there is 

 an additional point of interest, that the granules in the (glandular) 

 ectoderm cells differ from these," i.e., the granules in the Metschnikofi; 

 cells, " only in being of smaller size. I have been very slowly and 

 gradually led to the conclusion that the bodies in question, which I 

 propose to call ' Metschnikofi: cells,' are metamorphosed collar cells ; 

 that by their reaching to the exterior and becoming perforated, 

 pores are formed ; and that the granules of these and of the ecto- 

 derm, and of the glandular ectoderm in general (and possibly the 

 granular cells so frequently described beneath it in Silicea), are ex- 

 cretory." 



This latter proposition, so far as concerns Ascetta, may now be 

 considered proved, and I think the observation sufficiently important 

 to justify my asking permission to communicate it to the Society. 

 Leaving a sponge in a solution of indigo- carmine in sea-water (at 

 first I used a saturated, but afterwards a weaker, solution), I found 

 that the granules normally present in the Metschnikofi: and ectoderm 

 cells become replaced in part by dark-blue granules, no other part of 

 the sponge being in any way coloured blue. Fig. 1 shows a Metsch- 

 nikofi cell from a specimen of Ascetta clathrus, which had been 

 thirteen hours in saturated indigo- carmine solution. The black dots re- 

 present the granules which were blue, the colourless circles those which 

 were of the usual yellow ; a few of intermediate shading represent 

 granules which appeared pale-blue or green. Focussing showed that, 

 while this cell stretched under the spicule into the deep parts of the 

 sponge wall, the left-hand extremity emerged on the upper (ecto- 

 dermal) surface. 



This particular cell I had the pleasure of demonstrating, while 



* ' Quart. Jl. Micr. Sci.,' Oct., 1891, Review — Subsequently reprinted, by 

 the permission of Messrs. Churchill, under the title of 'Notes on Calcareous 

 Sponges.' 



