PORIFERA. III. ,! 



spirit) is whitish yellow, sometimes somewhat greyish. The surface has, as commonly in the genus 

 Grayella, a very characteristic aspect, being densely beset with pore-areas. These areas are circular 

 or generally oval and have a slightly elevated edge which surrounds the somewhat immersed pore- 

 membrane. Such is the structure in the specimens which are least contracted, but as a rule the 

 sponge is more highly contracted, and then the pore-areas become indistinct or are only seen as small 

 tubercles, and when the sponge is very strongly contracted they nearly quite disappear, and at the 

 same time the surface becomes rugose or wrinkled. For the rest the surface is all but smooth, the 

 spicules not being projecting or only to a very slight degree. The dermal membrane is in the pore- 

 areas a thin membrane, between the areas it is not sharply bounded inwards, and it is here richly 

 provided with spicules. Pores and oscula: The pores lie in the mentioned pore-areas in a number of 

 about ten or more in each area, they are circular or oval and were measured from quite small up to 

 0-09 mm in largest diameter; the pore-areas have a greatest size of 0-5 mm . The oscula are spout-shaped, 

 as the opening is surrounded by a conical collar, supported by spicules. The number of oscula is 

 various, in the small specimens there is most frequently only one osculum, which is then placed at 

 the upper end, but in the larger specimens there are several oscula, in a single specimen even eight. 

 The canal system seems to be very lacunous; there are especially extended cavities somewhat below 

 the surface, and they are extended somewhat parallel to the surface; they evidently belong to the 

 excurrent system, as they are in direct connection with the oscula. If a piece of the skin is cut off, 

 the openings of the incurrent canals, which are vertical to the surface, may be seen below the pore- 

 areas by aid of the microscope. These structural features are tolerably observable, when the sponge 

 is not too strongly contracted, but often the specimens are contracted to so high a degree, that these 

 structures are quite indistinct, at the same time that the pore-areas on the surface are closed and dis- 

 appearing. The sponge is evidently able to contract itself very strongly, and even the least contracted 

 specimens in my material are certainly contracted to no slight degree; the structures seem to show 

 that the)- are able to be considerably more distended, and the inner cavities, the pore-areas and the 

 canals are in this state certainly considerably larger. 



The skeleton: The dermal skeleton consists of close-lying, tangential acanthostyles, which lie 

 in more than one layer; they are only found in the membrane between the pore-areas, while the 

 membrane of the pore-areas themselves is quite devoid of them; they do not form any real reticulation 

 but by their arrangement around the pore-areas a kind of network is however formed. In the pore-mem- 

 brane, as said, no acanthostyles are found, but here chelae occur in great numbers. The main skeleton 

 is of a dendritical structure; upwards through the peduncle and up towards the upper end of the 

 sponge goes a spicula-axis, and from this fibres issue which go out to the surface and at the same 

 time branch somewhat; outermost they are spreading and support the dermal membrane, but do not 

 project beyond the surface; as the outermost spicules in the fibres do not go to the pore-areas, but 

 only to the membrane between them, the}' become partly arranged circularly around the pore-areas, 

 as may be seen, when a piece of the skin is cut off and examined from above. A transverse section 

 of the sponge shows the fibres radiating regularly from the axis to the surface. Between the fibres 

 no connecting fibres are found, but some scattered spicules occur between them; these spicules 

 are all acanthostyles, while the fibres are formed exclusively of tornotes. Downwards on the peduncle 



