and two EsperiadEeyrom the West Indies. 275 



isodictyal or polyhedral meshes of Acarnus imiominatus 

 (fig-. 4, a a «), where from two to six are placed side by side 

 and end to end for tliis purpose ; and where they join, their 

 ends are imbedded in a mass of sarcode densely charged with 

 the minute anchorate spicules, amidst which are a considerable 

 number of tricurvate or bow-like ones, all of which, united 

 together, afford support to the bulbous ends of sometimes as 

 many as twenty-four large capitate spicules, together with a 

 few of the smaller capitate ones, which are not more than half 

 the size of tlie former, and very sparsely scattered (fig. 5). 



The capitate spicules are termed by Dr. Bowerbank " de- 

 fensive," the anchorate " retentive," and the tricurvate or 

 bow-like '' tension spicula." 



Among other offices, the former are supposed to be for 

 catching " intruding worms " (p. 23), the anchorates for re- 

 taining the sarcode, and the latter to aid in expanding it. 



How far such offices are imposed upon these spicules re- 

 spectively in the present species the reader may conceive, 

 where the capitate sjiicules are situated in cavities to which 

 only the minutest particles are admitted, and the other spicules 

 confined to the knots of the skeleton, where at least no tension 

 whatever seems to be required ; or how these purposes are 

 fulfilled in sponges where there are no such spicules present, 

 as in the Chalineaj, in which the spicules are entirely within 

 the fibre, or in Verongia^ where there are no spicules at all, he 

 may also conjecture. 



In short, it is only when the sponge is in a passive state, or 

 dead or dried, that the ends of the spicules are uncovered by 

 the sarcode. In the active living state, the sarcode invariably 

 creeps ^^p to the tops of them gradually, until the whole are 

 concealed or thus invested. Hence the necessity of studying 

 sponges generally in their active, living state, before attempt- 

 ing to assign uses to their different spicules, which under any 

 circumstances are so self-evident in themselves, or so hidden 

 altogether, or so indefinite, that to enter upon the subject 

 savours more of weak twaddle than of useful description, and 

 so perplexes the student, usque ad nauseam, that every mo- 

 ment he is inclined to throw away the book, exclaiming with 

 the lawyers in court, " Give us your facts ; we don't Avant 

 your reasons." 



The capitate spicules arc present in all stages of develop- 

 ment in Acarnus innominatus, as Dr. Bowerbank has well 

 illustrated in his figures 73-76 inclusively. 



From exposure and other causes, the specimens of this 

 sponge had become more or less incrusted with calcareous 

 material, which required to be dissolved off by an acid before 



