OF THE SPONGIADjE. 131 



describing the detached cells and cilia, says, " At first the 

 polymorphism of the cell and movements of the tail are so 

 rapid, that literally, neither ' head nor tail' can be made out 

 of the little mass. Presently, however, its power of pro- 

 gression and motion begins to fail, and if separated from 

 other fragments it soon becomes stationary, and after a little 

 polymorphism assumes its natural passive form, which is 

 that of a spherical cell. During this time the motions of 

 the tail become more and more languid, and at length 

 cease altogether." The author continues, " If on the other 

 hand, there be very large fragments in the immediate 

 neighbourhood, or an active sponge-cell under polymor- 

 phism sweeps over the field, it may attach itself to one or 

 the other of these, when its cell becomes undistinguishable 

 from the common mass, and the tail floating and undulating 

 outwards is all that remains visible." This observation is 

 important, as it accounts in a great measure for our inability 

 to find the cilia in situ in the living and active condition 

 of the Spongilla ; and if the structure and imbedment of the 

 basal cell in the marine sponges be like those in that genus, 

 the same results would probably arise in the marine species, 

 rendering it extremely difficult, if not impossible, to detect 

 these organs in situ and in action. 



Lieberkuhn, in his paper in Muller's 'Archiv,' 1856, 

 pp. 1-19, 319-414, gives an account of the cilia and their 

 cells in situ. He describes them as forming a single layer 

 of spherical cells, ~ millim. in diameter, and which, though 

 touching each other, are not in such contact as to lose their 

 rounded figure. Lieberkuhn's description of the mode of 

 disposition of these cells in Spongilla would serve equally 

 well for those in Grantia compressa. Professor Huxley, in 

 a paper " On the Anatomy of the Genus TetJtya" published 

 in the 'Annals and Mag. Nat. Hist.,' vol. vii, p. 370, 

 describes cells and cilia from an Australian sponge, which 

 he designates spermatozoa, and which he describes as 

 having " long pointed, somewhat triangular heads, about 

 j^th of an inch in diameter, with truncated bases, from 

 which a very long filiform tail proceeds." These bodies 

 are figured in Plate XIV, vol. vii, fig. 9. 



