82 ANATOMY AND PHYSIOLOGY 



somewhat larger in size ; one of the largest measured ^ 

 inch in diameter, and a small one ^ inch : they are repre- 

 sented in situ in Fig. 282, Plate XVI. 



The most complete development of cellular structure 

 exists in the genus Grantia, where we find them lining the 

 great interstitial cavities of the sponge, as represented in 

 Pig. 812, Plate XXI, — each, probably, in a natural and 

 healthy condition sustaining a cilium. ' The nucleus in each 

 cell is constantly present, and strikingly apparent when 

 viewed vrith a power of linear, as represented in Pig. 314, 

 Plate XXI. The only instance with which I am acquainted 

 of a conjoined arrangement of such cells exists in the enve- 

 lope of the ovaries of 8pongilla Carteri, the species described 

 by Carter in his ' Account of the Freshwater Sponges in 

 the Island of Bombay,' which that author believed to be 

 Spongilla friahilis, Lamarck, but which proves to be a dis- 

 tinct species, which I have named after its discoverer, as 

 a slight recognition of the good services he has rendered to 

 science by his excellent and accurate observations. These 

 cells may be detected in situ after the envelope of the ovary 

 has been submitted for a very short time to the action of 

 hot nitric acid, so as to render the coriaceous envelope 

 semi-transparent without destroying it. The structure of 

 its walls is then seen to consist of linear series of cells, six 

 or eight in length, closely packed together in lines radiating 

 from the centre of the ovary to its external surface. They 

 do not appear to be absolutely in contact with each other, 

 but are usually seen to be separated by a thin stratum of 

 a transparent substance, probably an indurated membrane 

 or sarcode. At the surface of the envelope they frequently 

 appear to be somewhat hexagonal from mutual compres- 

 sion. I could not detect a nucleus in any of them (Fig. 284, 

 Plate XVI). Carter and other writers on Spongilla have 

 designated the granulated forms of the sarcode in those 

 sponges, " Sponge cells," but I cannot coincide with that 

 opinion. I have frequently tried in vain to detect a proper 

 coat of cellular tissue on the Amoeba-hke granular masses 

 into which Spongilla fluviatilis resolves itself at certain 

 periods of its existence, and neither in a healthy and active 



