186 A MONOGRAPH OF THE 



At the latter end of August, 1859, I received two speci- 

 mens of this sponge from the Rev. A. M. Norman, who 

 dredged them up in the neighbourhood of Guernsey. The 

 largest of these was one and three qua)'ters of an inch in 

 length, one and a quarter inch in breadth, and half an inch 

 in thickness ; the smaller one somewhat less in its dimen- 

 sions, but the surface of each was prominently and abun- 

 dantly mammillated, and especially the smaller of the two. 

 In the larger of the two specimens, particularly on the 

 corrugated portions of the surface, the positions of the 

 pores were distinctly visible by the aid of a lens of two 

 inches focus, and with a higher power they presented the 

 appearance of minute pits, but they were not to be detected 

 by the same means on the surface of the smaller of the 

 two specimens. 



The hispid character is not visible by the aid of a hand 

 lens, but when a section at right angles to the surface is ex- 

 amined with a power of about 100 linear, it is seen to be pro- 

 duced by the projection at about right angles to the surface 

 of an infinite number of small sub-fusiformi-acuate spicula. 



In the largest of Mr. Norman's specimens there were 

 two minute oscula in an open condition, on the corrugated 

 surface of the sponge ; they were simple circular orifices, 

 with this exception, I could not detect these organs in an 

 open state, but longitudinal and transverse sections of the 

 apices of the mammillae appeared to indicate their position 

 at those points, beyond a reasonable doubt. The pores 

 were also in a closed state, but their positions were indi- 

 cated by the numerous little areas, free or nearly free from 

 spicula, which abound in the dermal tissue. 



The crustular character of the dermal tissue is not pro- 

 duced by a peculiar arrangement of the organic tissues, but 

 it is caused by a more condensed state of a stratum of the 

 ordinary tissues of the sponge, and in this layer, beneath 

 each of the porous areas, there is an intermarginal cavity 

 to receive and convey the incurrent streams to the interior 

 of the sponge. 



It is not improbable that we may hereafter find that each 

 of the porous areas in the dermal membrane may have 



