298 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



The Albatross sponge is more or less spheroidal, about 15 mm. in 

 diameter, attached to the inside of a Crepidula shell. The color is 

 dark brown at the surface, lighter below the ectosome. There are two 

 small oscula about V4 mm. in diameter on the upper surface near the 

 equator. 



Thiele says (1900, p. 31) in three of his specimens the pores are in 

 closely set, commonly oval, areas, the intervening trabeculae forming 

 a network. A fourth specimen, tentatively assigned to a variety, 

 micropora, had inconspicuous, much smaller, pore areas. 



Over a part of the surface of the Albatross specimen similar pore 

 areas are visible to the eye as closely set small whitish patches sep- 

 arated by the brown ectosome. Such areas are about 300 \x or less in 

 diameter, angular in shape, sometimes rosette-shaped — namely, with 

 rounded lobes ; about 6-7 pores in an area, pores about 20 \i. in diam- 

 eter. The intervening trabeculae of ectosome may be as wide as, or 

 narrower than, the areas. Where such areas are most distinct the 

 pores are for the most part closed. Elsewhere on the surface of 

 this specimen the pores are fully open and " pore areas " do not 

 exist. Instead the entire dermal membrane is uniformly riddled 

 with pores. Through it ectosomal trabeculae separating the sub- 

 dermal spaces can be vaguely seen. Transitions between these two 

 states occur and it is clear that they represent different physiological 

 phases. That is, where the sponge is expanded and the pores all 

 open there are no areas. As the sponge loses water and the pores 

 close, " pore areas " appear. Doubtless the events are about as 

 follows : Above the larger spaces in the ectosome, what are denomi- 

 nated the subdermal chambers, the pores are slow in closing. In the 

 regions between such spaces the pores close first of all and the pig- 

 ment cells quickly invade the dermal membrane from the deeper 

 strata of the ectosome. This brings on the appearance of brown 

 trabeculae separating the " areas." 



A further inspection of the surface of this sponge shows that as 

 the pores continue to close quite small areas including only two or 

 three pores may be left, well separated by brown ectosome. Doubt- 

 less the specimen for which Thiele suggests the name, var. micropora, 

 was in this phase when preserved. It seems probable that after com- 

 plete and prolonged closure of the pores the whole surface of the 

 sponge might become uniformly brown. It can not be said that the 

 ;t pore areas " make a specific mark, for they may or may not be 

 there. "What is possibly specific, however, is a general and subtle 

 complex of anatomy and habit which results in the appearance of 

 pore areas in a certain physiological phase. 



As in Thiele's specimens, the ectosome is about 300 \x. thick and 

 contains an abundance of spheruliferous pigment cells. These ex- 

 tend into the choanosome along the radial skeletal bundles. The 



