28 



THE SPONGES OF THE WEST-CENTRAL PACIFIC 

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Text Figure No. 14. Surface view of Druinella tyroeis, X 182. The dermal fiber shows, 



outlining one skeletal pore and portions of three others. Near A appear five of the real 



or protoplasmic pores piercing the dermal membrane. 



The color in life was white, tinged slightly with yellow, but the sponge 

 has darkened to walnut brown after several months preservation in alcohol. 

 The color of the endosome was the same as that of the exterior. The con- 

 sistency was exceedingly like that of cheese, both when felt and when cut 

 by a knife. 



The surface is conulose, the conules 1 to 3 mm high and about 4 mm 

 apart. The skeletal pores show plainly to the naked eye and are about 350 /x 

 in diameter, about two of them for each square mm of surface of the sponge. 

 These skeletal pores are filled in with protoplasmic membranes, within which 

 finer pores appear. The latter close quite readily, are round when opened, 

 and are 20 /x to 40 n in diameter. They are very irregularly distributed inside 

 the membrane or skeletal pore, considerable regions of each such membrane 

 being devoid of openings. The oscules are not set apart from inhalant openings 

 and therefore are confused with them. 



There does not seem to be any all-pervasive ectosome in this species, 

 but a dermal membrane may be considered as being represented by the above- 

 mentioned protoplasmic sheet, which fills in the skeletal pores. The endo- 

 some is very dense, both with flesh and fibro-reticulation. It contains scat- 

 tered foreign spicules. The histological structure is quite remarkable. The 

 flagellate chambers are very small, only about 20 /a in diameter, and are absent 

 from considerable areas. These areas are full of strands, 6 fx in diameter, 



