Sponge-fauna of Norway. 253 



walls of the endochone consist almost entirely of muscular 

 tissue. From the various states in which the endochone 

 occurs in different cases, sometimes almost entirely obliterated 

 by the closure of its muscular walls, sometimes continuous in 

 one and the same straight line by the widely open state of 

 the intervening sphincter, one may infer that it behaves as a 

 part of the sphinctral muscle : when the upper portion alone 

 of this muscle contracts we have the condition of things 

 represented in PI. XI. fig. 7 ; when the whole contracts, that 

 represented in PL XII. fig. 30, where the endochone has 

 become constricted to a mere narrow tube ; while, should the 

 sphincter remain altogether relaxed, we have the form shown 

 in PI. XI. fig. 23. 



The muscular fibres of this sphincter have here, as in Stel- 

 letta Normanij a character very different from that of the other 

 fusiform fibres of the cortex; the axial threads are much thicker, 

 the hyaline exterior is reduced in quantity, and the whole muscle 

 has a less transparent and much greyer appearance than in 

 the other case. Moreover the fibres of the lower face of the 

 cortex do not stain deeply with carmine, while those of the 

 sphincters acquire an intense colour with this tinction-reagent. 

 Finally, the latter are so arranged that they can and evidently 

 do contract, and thus are true muscles both by function and 

 structure ; while the former occur in such places and arranged 

 in such a manner that it is difficult to understand how, in 

 this sponge at least, they could contract, or what purpose i 

 would serve if they did. Thus, altogether, I begin to doubt 

 how far it is justifiable to extend our ideas as to the nature of 

 the sphinctral fibres to those of the lower cortex, and am 

 much more inclined to regard the latter as forming a kind 

 of fibrous connective tissue, and the former alone as true 

 muscles. 



Before leaving the subject of the chones it would be but 

 fair to the memory of Bowerbank to bear our testimony to the 

 striking fidelity which characterizes his representation of the 

 structure of these organs — a fidelity which is the more striking 

 when we consider the comparatively small size which they 

 possess in this species, and recollect the imperfect methods 

 which this much-abused observer had at his disposal. 



3. The Subcortical Crypts. — Compared with those of Stel- 

 letta JSormanij the crypts beneath the general surface of the 

 sponge are of very trifling dimensions ; but beneath the sur- 

 face which gives attachment to an adhering foreign sponge 

 they become abnormally large, attaining a length four or five 

 times that of the average. This probably is a pathological 

 peculiarity due to the disturbance of the normal water-circula- 



