290 A MONOGRAPH OF THE 



the ovarian vesicles of the Zoophyte were not in connection 

 with their parent body, and on many of them so great a 

 number of spicula had been deposited, that the illusion 

 was very strong in these cases. The like intermixture of 

 the ovarian vesicles with the structures of a specimen of 

 Isodictya Clarkei taken from the same Zoophyte was 

 observed ; but the vesicle in this case, although detached 

 from the Zoophyte, and immersed in the body of the 

 sponge, had very few spicula deposited on their surface. 



This curious case is instructive, as it shows us how 

 readily we may be deceived by the common habit of the 

 parasitical sponges of appropriating in various interesting 

 modes the parts of the plants or Zoophytes on which they 

 are based, to the purposes of their own development or 

 preservation. 



11. Isodictya indtstincta, Bowerbank. 



Sponge. Massive, sessile ; surface smooth. Oscula simplci; 

 or more or less elevated. Pores visible, congregated 

 in irregular areas. Dermal membrane aspiculous. 

 Skeleton. Primary lines multispiculous ; secondarj- 

 lines unispiculous, irregular; spicula acerate, short; 

 and rather stout; rarely acuate. Interstitial mem- 

 branes. Tension spicula acerate, slender, few in' 

 number. 



Colour. — Alive, pallid ochreous yellow; dried, dark brown. 



Habitat. — Orkney, Captain Thomas, R.N. Exmouth, 

 Mrs. Griffiths. Guernsey, Rev. A. M. Norman. Hastings,, 

 J. S. Bowerbank. 



Examined. — Alive and dried. 



I have received four specimens of this species, two from 

 my friend Captain Thomas, of the hydrographical sui-vey, 

 dredged at the Orkney Islands in 35 fathoms; one from 

 the late Mrs. Griffiths, who obtained it from Exmouth ; and 

 one from the Rev. A. M. Norman, from Guernsey. This 



