THE SPONGES. 23 



or dermal surface, is not present, possibly owing to the biid preservation of 

 the specimen. The root spicules have been pulled out. The wall of the 

 cup is excavated by numerous canals 4 mm. and less in diameter, and the 

 consistency of the sponge is soft and flabby. The dermal membrane is 

 badly injured, the gastral membrane less so. The latter is not separated 

 from the sponge tissue, but simply passes over the apertures of numerous 

 efferent canals. 



The parenchymalia principalia are chiefly oxydiacts, which vary greatly 

 in size and considerably in details of shape. There are many slender, 

 often slightly curved, nearly cylindrical forms, with slight enlargement at 

 or near the middle showing an axial cross. Common sizes are 1.5 to 2 mm. 

 long by 20 fji thick. The ends are sometimes rounded and slightly enlarged. 

 The spicule really tapers slightly from the middle toward the ends, and 

 when the length is short (0.5 to 1 mm.) the outline becomes noticeably 



fusiform. There are some similar but much larger forms, connected 



by intermediate stages with the above. These may reach a size of 6 mm. 



X 34 /x. There is no median enlargement. There are other stouter 



diacts of a distinctly fusiform shape, ranging in size from 600 /x x 20 /x to 

 1350 /x X 60 /x. These exhibit an enlargement with axial cross. The 

 enlargement may be faint or conspicuous, and may or may not extend 

 quite round the spicule. This diact is not common in the interior, but is 

 the predominating form at the dermal and gastral surfaces. 



Other principalia are smooth oxyhexacts, which are scattered through 

 the parenchyma in some number. The rays, which are not always of the 

 same length, commonly range from 200 to 850 /x in length. A consider- 

 able number of large forms are present, having a ray length up to 3.5 mm. 



The hypodermal and hypogastral pentacts are alike, and are strong, 

 smooth oxypentacts, with no remnant of the distal ray. The tangential 

 rays commonly vary in length from 350 to 850 /x. The proximal ray may 

 be somewhat shorter than, or two or three times as long as, the tangentials. 



Micro-oxyhexacts are abundant throughout the parenchyma. The spic- 

 ules are strong spicules with rays 40-60 /x long and 3-4 fx thick at the 

 base ; commonest size of ray about 50 /x x 4 /x. Very minute, sharp den- 

 ticulations are scattered along the ray, which tapers to a fine point. 

 Spicules the rays of which are slightly curved, as in Plate 2, Fig. 10, 

 predominate, but abundant straight-rayed spicules (Plate 2, Fig. 11) 

 occur, and not infrequently spicules are met with in which the rays are 



