SP0NG1IDA. 
14 Spcm g. 
made by which the area occupied by pores is determined to be *096 
of that of the surface of the Sponge, and 22 times that of the oscular 
openings, showing a great difference to exist in life between the 
rapidity of inhalation and exhalation of water. The spinispirular 
spicules appear to lie in the ectoderm. The mesoderm on the face of 
the other two layers exhibits fibrils resembling nerve-fibres. The matrix 
surrounding the processes of the mesoderm cells is sometimes fibrillated ; 
at a short distance below the dermis, occurs a layer of connective-tissue 
cells, containing strongly refractive globules ; the globules are perhaps 
albuminoid in nature ; the sphincters of the water-canals are composed 
of fusiform mesoderm-cells, occasionally longitudinally striated ; the 
sperm-balls are distributed throughout all the Sponge, except the neigh- 
bourhood of the surface. The hooks of the anchoring spicules are 
developed late, and appoar as mere spines, accompanied by no terminal 
inflation of the spicule. 
Thenea muricata. Under this name, Yosmaer, (17) p. 5, pis. i. figs. 1-8, 
ii. figs. 1-21, iv. figs. 114 & 115, includes Tethya muricata , Bowerbank, 
Tisiphonia agariciformis, Wyville Thomson, Tethyopsis columnifer , 
Stewart, Wyvillethomsonia wallichi , Wright, Tisiphonia fenestrata , 
Schmidt, besides other synonyms given with more or less certainty. 
Found up to 7G° N. lat., and 45° E. long. Form described ; symmetry 
remarked upon. The various forms of the pore-bearing horizontal furrow 
attributed to contraction ; it is probably a special inhalant organ; the 
variation in the condition of the rooting-fibres is possibly connected with 
variations in the nature of the bottom. Yosmaer considers the specifi- 
cally important spicules to be the acerate, the ternate with bifurcating 
rays, the simple ternate, the stellate, and the elongo-stellate ; he describes 
the different modifications. Three varieties are distinguished under the 
letters o, 0 , 7 , partly by the external form, partly by the spicules ; a is 
represented by Tisiphonia fenestrata , Schmidt, £ by Tethea muricata , 
Bowerbank. 
Craniella merged in Tetilla, by Sollas (15). 
Tetilla. Described species enumerated by Sollas, l. c. pp. 160 & 427. 
T. cranium , 1. c. pp. 149 & 426, pi. vii. Histology, &c., described ; the 
hamate spicules lie in the ectoderm. The canal system shows ecto- 
and endochones; the incurrent canals branch much. It has a small 
osculum. Dermis delicate, extended between projecting spicular fibres, 
covering the wide intermarginal cavities; the ectoderm of these 
cavities is formed by polygonal cells, and appears to contain bacillar 
spicules. The outer membrane, or skin, appears to consist of a struc- 
tureless cuticula, covering a cellular ectoderm, but is itself perhaps 
also cellular during life. The mesoderm includes small round or 
oval cells and fusiform granular cells in strands or forming a thin subepi- 
dermal layer ; such fusiform cells form sphincter muscles for the in- 
halant water-canals, while a few are ranged radially around these 
canals. The medullary substance, or mark, consists (besides the canals 
and chambers) of a transparent matrix, charged with abundant minute 
refractive £ granules and a few nuclei, also fusiform fibres near the 
spicular bundles, &c., and some large granular amcebiform cells with 
