280 WILSON. Vion. 
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 
Pa ee of about ;7,5, mm. long, gan sigmaspires, and 
sigmas 1°. mm. long, large shovels ;% mm. and small shovels 
100 
~3._ mm. long. The small shovels abanane but large ones 
le sigmas and sigmaspires abundant, toxaspires less so. 
Oxytylotes scattered irregularly through the mesoderm, not 
united into a meshwork. In peripheral region the oxytylotes 
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 Holl, Mass. 
The body of the sponge consists of a network of narrow tra- 
beculae, separated by a system of canals, Pl. 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 
