144 THE SPONGES. 



Collenchyma is found in some abundance at the surface in the shape of 

 small, irregular, and vaguely defined areas, which in the uninjured sponge 

 are inconspicuous, although evident in preparations. As in the other 

 species of the genus, the skeletal reticulum is absent from such areas. In 

 the intervening regions constituting the greater part of the surface, the 



skeletal reticulum lies beneath the dermal membrane in the usual way. 



Preparations of the surface show that there is no constant relation between 

 the superficial collenchymatous areas and tlie presence of oscula. Tlie 

 latter, measuring commonly 300-500 /x in diameter, and occasionally 

 reaching a diameter of 2 mm., are scattered abundantly over the surface, 

 and occur both in the collenchymatous areas and in the intervening regions. 

 Smaller apertures of all sizes, from 35 jx to 300 /x in diameter, are also 

 scattered abundantly over the whole dermal membrane. The smaller are 

 doubtless pores. It is not, however, possible in this sponge to distinguish, 

 by their morphological characteristics alone, the smallest oscula from the 

 larger pores, since there is such a perfect intergradation in size, and since 

 the oscula and pores are both irregularly scattered. 



The flagellated chambers in the present condition of the specimens vary 

 in diameter from 2-4 to 32 /a. Some are spheroidal, others markedly com- 

 pressed. Their arrangement indicates them to be eurypylous. 



Sjncuh's. Merjasderes. 1. Style, Fig. 10, Plate 20. Spicule about 

 cylindrical, slightly curved, very sparingly spinose throughout its length; 

 pointed end sometimes rounded. Size, 440 /a x 20 /a. 



2. Subtylote, Fig. 11, Plate 20. Spicule very slightly, sometimes not, 

 enlarged at the ends ; smooth, except at the extreme end, where it is feebly 

 spinose. Size, 315 /a x 8 ju. 



Microscleres. 3. Bipocillus 16-20 yx long, Plate 20, Fig. 2, a, c, d. 

 The curved axis terminates at one end in 2 or 3 pointed teeth, which 

 project toward the opposite extremity. At the other end the axis ter- 

 minates in a thin plate-like expansion with spherical curvature, divided 

 by one or two narrow incisions into 2 or 3 lobes. Axis has a ventral keel, 

 which disappears toward the toothed end. On each side of the keel, axis 

 thins away, forming a lateral flange, which is sharply marked off from 

 the terminal lobe of that side by a rounded incision. 



4- Anisochela 12-20 /x long, Plate 20, Fig. 2 h. Spicule of the pal- 

 mate type, with a little spine at the small end. 



Skeletal Arramjeinad. The main skeleton (Fig. 1, Plate 24, a section 



