28o WILSON. [Vol. IX. 



perforated by closely set pores. Surface appears porous to the 

 eye, owing to abundance of comparatively deep subdermal 

 cavities, which when magnified appear as pore-riddled areas. 

 Between such areas the pores are inconspicuous. Oscula 

 fairly abundant and small, often leading into wide shallow 

 spaces, covered with imperforate membrane. Sponge body 

 consists of network of trabeculae, containing single rows of 

 closely set flagellated chambers. Spicules include smooth 

 o.xytylotes of about -^-§-^ mm. long, toxaspires, sigmaspires, and 

 sigmas JgO^ mm. long, large shovels ^^1^ mm. and small shovels 

 j-|-jj mm. long. The small shovels abundant, but large ones 

 rare ; sigmas and sigmaspires abundant, toxaspires less so. 

 O.xytylotes scattered irregularly through the mesoderm, not 

 united into a meshwork. In peripheral region the o.xytylotes 

 form radial bundles, which divide into brushes supporting the 

 dermal membrane. In the body of sponge, spicular bundles 

 are few in number and without order in their arrangement. 

 Wharf piles, Woods Hall, Mass. 



The body of the sponge consists of a network of narrow tra- 

 beculae, separated by a system of canals, PI. XIV, Fig. 2. Esper- 

 ella is one of those sponges in which there is no symmetrical 

 arrangement of parts, and which offer the greatest difficulty to 

 the solution of the question as to what constitutes the typical 

 structure of a sponge individual. For in such a sponge neither 

 the oscula, pores, nor canals, are arranged in such a way as to 

 indicate the division of the body into regions which could be 

 compared with one another, and so be taken as the represent- 

 atives of individuals. 



The canal system belongs to Vosmaer's third type. The 

 distinguishing features of the canal system are that all the 

 canals, afferent as well as efferent, are so wide and spacious. 

 Each chamber has not a special afferent canal of its own, but 

 many chambers are grouped round a single comparatively wide 

 afferent canal into which they open directly. Similarly there 

 is no special efferent canal for each chamber, but many cham- 

 bers open directly into a wide canal. 



The development of numerous wide and for the most part 

 comparatively shallow, afferent canals directly beneath the skin 



