On Dactylocalyx pumiceus (Stutchhury). By W. J. Sollas. 125 



caused to enter at the inhalent orifices, to pass through the fine 

 canals, and finally to empty itself out of the sponge by the 

 excurrent tubes. But having regard to analogy, one cannot but 

 feel that a similar mechanism once existed in our specimens of 

 Dactylocalyx : the minute canals which unite together the ultimate 

 ramifications of the excurrent and incurrent tubes, were the seat of 

 those ampullaceous sacs which by driving the water continually 

 out at one end of the minute canals, caused a continual influx at 

 the other ; the single current entering at one inhalent apertui-e was 

 immensely subdivided to supply a large number of ampullaceous 

 sacs ; the many currents leaving those sacs were united together to 

 flow out at an exhalent aperture in a single stream. 



Skeleton. — On examining the skeleton of the sponge with the 

 naked eye, one observes a regular network of fibres, the meshes of 

 which may be called " large " meshes to distinguish them from 

 others of which we speak next ; similarly, the fibres may be known 

 as " large " fibres. 



Under the Microscope the large fibres are found to consist of a 

 network of much finer fibres, and with correspondingly small 

 meshes. These are what are usually understood as the meshes and 

 fibres of the skeleton, so that the terms may be used without any 

 distinctive quaUfication. 



The large meshes may possibly serve in some cases to give 

 passage to the minute ramifications of the water-canals of the 

 sponge. 



Dermal layer. — Bowerbank states that he could not find any 

 trace of dermal structure in the half of the type specimen which he 

 examined, but predicts that when a specimen perfect enough to 

 show it is obtained, it will present the characters of the same 

 structure in Dactylocalyx Prattii or D. Masuni. Unable to 

 believe that the work of cleaning so large a specimen as ours could 

 have been so thoroughly accomplished as to have removed all 

 vestiges of the dermal skeleton, I set to work to find the missing 

 structure, being at the same time well assured that if found it 

 would not in a Hexactinellid sponge Hke D. pumiceus present the 

 same characters as in Lithistids such as D. Prattii and D. Masoni. 

 Nor did I have long to look, for down in a tubule, which com- 

 pletely perforated the sponge, a perfect forest of long acerate 

 spicules was seen, bristling erectly from the surface, and forming, 

 together with a layer of sexradiate spicules, the structure of our 

 search. This tubule, as already remarked completely perforates 

 the wall of the sponge, passing freely from one side to the 

 other ; it thus difiers from an ordinary excurrent or incurrent 

 canal, and in all probability represents a part of the surface of 

 the edge of the sponge, which became simply enclosed by growth 

 and not incorporated with the body substance. If this is so, 



