PLATE I. 



The foliated forms of this species are well repre- 

 sented in Dr. Johnson's ' History of the British 

 Sponges,' plate sx, fig. 1. 



In the ' Transactions ' of the Microscopical Society, 

 vol iii, illustrating my paper " On the Ciliary Action 

 in the Spongiadse," there is figured on plate ix, fig. 

 1, a section of a small specimen of 0. compressa at right 

 angles to the axis of the sponge exhibiting the ciliated 

 cells in situ; and fig. 2 in the same plate represents 

 a portion of the inner surface of the sponge ; the 

 central group of three diaphragms (a) exhibits the 

 appearance of the cilia when slowly in motion within 

 the diaphragm. Fig. 3 represents detached tessellated 

 cells, and fig. 4 detached tessellated cells and cilia. 



