sponge-fauna of Norway. 441 



The total area of tliese is 0'58216 square inch ; and 

 6 : 0-58216 = 1 : 0-097, 

 i. e. 1 square inch of the sponge-surface contains 0"097 square 

 inch of pore-area. 



In the second — 



(i.) The area of the sponge-surface taken (in the sketch) 



was 1-5 square inch, 

 (ii.) It contained twelve pores, two of 0-2, two of 0-15, and 

 eight of 0-1 inch in diameter. 



The total area of these is 0-14283 square inch ; and 



1-5 : 0-14283 = 1 : 0-095, 



a close correspondence for two quite independent determina- 

 tions, and remarkable considering the difference in the average 

 size of the pores measured in the two cases ; it would appear 

 tliat the smaller pores made up in number for what they lacked 

 in magnitude. Taking the average we obtain 0'096 : 1 as 

 the ratio of the poral to the general area ; and the number 

 0'096 may be called the pore-index of the sponge. 



We have next to ascertain the relative size of the total 

 poral to the total oscular area. The specimen on which the 

 preceding observations were made measures 4-084 inches in 

 circumference and 0-8 inch in height ; it may be regarded as 

 formed by two equal segments of a sphere 0-9 inch in dia- 

 meter, each 0-4 inch high, and thus has a superficial area of 

 2-26 square inches, ]\J ultiplying 2*26 by 0'096, the poral 

 index, we have 0'172 square inch as the total poral area ; so, 

 if all the pores were to coalesce, they would form a single 

 aperture under one fifth of a square inch in area. This, how- 

 ever, is an underestimate, since no account has been taken of 

 the larger number of pores in the equatorial recess. 



The oscule is 0-1 inch in diameter, or 0-007854 square 

 inch in area; and the oscular (O) is consequently to the 

 poral (P) area as 



0-007854 : 0-172 = 1 : 22. 



P 



••• 0=22. 



This number may be conveniently styled the poral-oscular 

 index. Its determination is here ])robably a little too low ; 

 but it suffices to show tliat, with an almost imperceptible influx 

 of water into the pores of the sponge, there may be a very 

 lively discharge from the oscule. A determination of the 



P 



value of — was made in a second specimen, unfortunately a 



