206 Mr. H. J. Carter oii the Position of the 



This having been established, let us now endeavour to trace 

 the nutrient particles from the excretory canals into the 

 ampullaceous sac, and this can be best inferred by finding 

 out the position of the ampullaceous sac and its relation to 

 the excretory canals. 



When describing in a general way the structure of a 

 sponge, in the introductory remarks to the order Psammo- 

 nemata among Mr. Wilson's Australian specimens ('Annals,' 

 1885, vol. XV. p. 209), it was observed that " what has been 

 stated of the external parts of the sponge applies ccet. par. to 

 the internal ones or parenchyma ; for as the sponge grows by 

 the addition of layers to its circiuiiference, that is radiatingly, 

 so the surface of to-day becomes part of the internal structure 

 of to-morrow, and thus somewhat modified it passes into a 

 cancellated form, which is the parenchyma ; that is to say, 

 the fibrous skeleton, cored by mineral material or not, becomes 

 a solid mass of reticulation, in which the interstices are tympa- 

 nized by the still poriferous sarcode (as may be seen in a 

 dried specimen), and the cancellated chambers thus completed. 

 Lastly, the whole is traversed by the branches of the excre- 

 tory canal-systems. I use the latter in the plural number, 

 because generally every vent indicates a system." 



Kow here, if 1 had had the information which I now possess, 

 it might have been added that the " tympanizing sarcode " 

 was charged with ampullaceous sacs and pierced by a num- 

 ber of pores or small holes, which would have so far completed 

 the general description of sponge-structure. But this infor- 

 mation has come to me since, partly from a microscopic ex- 

 amination of the tympanizing sarcode in a dry specimen, and 

 partly from that of a small wet one closely allied to Wilsonella 

 australteyisis, which will be more particulaily described here- 

 after. 



In this small specimen, which hardly exceeds in size an inch 

 each way, the ampullaceous sacs, averaging 20 to 30-6000ths 

 in. in diameter, are imusually well preserved, apparently from 

 natural toughness ; but be this as it may, tliey present them- 

 selves under a clear form in which their general outline, as 

 well as that of the spongozoa of which they are composed, 

 is sharply defined ; moreover they stain well with blue 

 aniline ink, and in comparatively thin slices, that is about 

 l-24th to l-16th in. thick, become still more conspicuous 

 under this treatment ; so that when the slices are mounted in 

 glycerine and viewed with a magnifying-power of about 90 

 diameters, in a cell icithout compression, the ampullaceous 

 sacs can be distinctly seen to surround the water-canals, where 

 they are more or less approximated, apparently unmolested, 



