Sponge-fauna of Norway. 407 



type of " Astcanale " in the Leucones, and conjectured by 

 him to exist also in the rind-sponges; one has but to compare 

 the description given of this structure in the Leucones (' Die 

 Kalkschwamme,' p. 235) with that given here as regards 

 Isops, to see that there is no real resemblance between 

 them. 



Pathology. 



The exterior of the sponge is covered by various attached 

 foreign bodies, such as young sponges, both calcareous and 

 siliceous, minute Hydrozoa, Algge, and Foraminifera. A small 

 Waldheimia is also rooted into the sponge at one point, with- 

 out apparently causing much harm. The larger attached 

 Foraminifera are covered marginally by a thin brownish film, 

 which has extended onto their upper surface from the dermis 

 of the sponge. At its extreme edge this film only contains 

 stellate spicules ; but further on a few globates make their 

 appearance. It would appear that the sponge is making, in 

 these cases, an effort to overgrow and enclose the foreign 

 bodies. On touching one of the Foraminifera with a sharp- 

 pointed instrument, however, it separates from the sponge 

 with the greatest facility, bearing with it on its under surface 

 a number of attached globates, and leaving behind an irre- 

 gular pit in the cortex. If the removed globates, or those 

 immediately surrounding the pit left in the rind, be examined 

 uuder the microscope, it will be found that they have entirely 

 lost their fibrillar connective ligaments, which have degene- 

 rated into a quantity of granular material, probably of the 

 nature of pus. 



In the interior of the sponge foreign bodies also frequently 

 occur — diatoms, Radiolaria, foreign sponge-spicules, Forami- 

 nifera (both calcareous and arenaceous), and the fibres of the 

 Waldheimia-^eduncle. 



The siliceous inclusions and the fibres of the Brachiopod 

 are simply imbedded in the mark, without producing or suf- 

 fering any apparent change ; the calcareous Foraminifera, 

 however, lose the calcareous walls of their test by absorption, 

 some kind of hyaline material taking their place ; at the same 

 time the mark surrounding the tests and filling their chambers 

 becomes converted into gelatinous connective tissue. 



Turning, again, to the foreign ! bodies of the exterior, 

 one very singular case of commensalism remains to be noticed. 

 A small Geodine sponge, only just escaped from the larval 

 stage, has attached itself immediately over one of the incurrent 

 chones (PI. XVII. fig. l,p), and grown in such a manner that 

 the terminal opening of its single branched excurrent tube is 



