AmjyuUaceoiis Sac in the Spongida. 205 



evident that they were for the purpose of admitting water 

 into the sponge as well as the nutrient particles which it might 

 contain. Further confirmation of this was adduced, by in- 

 stancing the calcareous sponge TeicJionella lahyrinthica^ 

 wherein the wall is composed, as in the Sycones generally, of 

 hollow cylindrical chambers arranged transversely across it 

 and in juxtaposition, so that the pores are at one end and the 

 vent at the other, viz. on either side of the wall, respectively, 

 while the interior of the chamber is studded all over with 

 spongozoa ('Annals,' 1885, vol. xv. p. 119, pi. iv. fig. 7 

 &c.). At this time also I cited two other cases in Psammo- 

 nematous sponges, viz. in Geelongia vasiformis and Hirciuia 

 intertexta^ where the pores of tlie surface opened directly into 

 large excretory canals, that is, of course, through the mediura 

 of the subdermal structure. Next, viz. in 1886, I found it 

 most convincingly in a remarkable sponge from " Port Phillip 

 Heads " described under the name of Suberites insignis 

 (' Annals,' vol. xvii. p. 118), wherein the " sinus-like dila- 

 tations of the excretory canal-system " are only separated 

 externally from the water by the poriferous epidermis and 

 subjacent subdermal cavities which lie over tliem at this part. 

 Finally, in 1886, I described and illustrated this in PIdoeo- 

 dictyoa hirotuliferum, where the digital appendages of this 

 sponge are tubular and hollow, and their wall alone formed 

 of the poriferous and subdermal structures, without, so far as 

 I can see, the trace of an ampullaceous sac, so that the water, 

 with its nutrient particles, must pass directly into the cavity 

 of the process, and the nutrient particles be deflected to their 

 destination afterw^ards, which probably was in the body of 

 this sponge, of which I only possessed the tubular appendages 

 for description. Moreover, the innei- surface of the wall is 

 covered with a layer of epithelial cells like those of the surface. 



[It might be here stated that the " skin" of a sponge, so 

 to call it, generally consists of an epidermal or poriferous 

 layer and the subdermal cavities or subdermal structure — the 

 former very thin and composed of a layer of epithelial cells, 

 in which the pores are situated, and the latter comparatively 

 thick and composed of a cancello-clathro-fibro-membranous 

 structure, in which the intervals all communicate with each 

 other; that is, it would be a continuous hollow subdermal 

 cavity but for the presence of this structure. Then comes the 

 body-substance of the sponge, in which the ampullaceous sacs 

 begm to appear. It is the " skin " ojily which forms the 

 wall of the poriferous tubular processes of Phlceodictgon 

 hirotidiferuviJ\ 



All this shows that the pores are as much for aqueous cir- 

 culation as for the introduction of nutritive material. 



