338 H. JAMES-CLARK OX THE AFFINITIES OF SPONGES. 



from the surface like so many fine, rigid bristles. In fact, the motions of this animal are so 

 lightning-like in rapidity that I have never seen this form of cilia except when the body was 

 in a quiet state ; and therefore I judge that, as they do not move then, they are the principal 

 organs of locomotion. There is on the right side a group of much more heavily built cilia 

 (cl), which project from the oblique furrow in which the mouth (m) is set. They are more 

 particularly devoted to producing currents in which the particles of food may be brought to 

 the mouth. 



" We see, also, projecting from the forward end of the oblique furrow, and near the an- 

 terior edge of the mouth (m), one of those proboscis-like lashes (/) [&flagellvm\ which are so 

 characteristic of the lower, ciliate [flagellate] infusoria ; but yet it would not seem to have the 

 same office as in the latter, since it is usually held in this position, apparently as rigid as if it 

 were a wire ; and only now and then does it move, by a sudden jerk, and disappears in the 

 oblique furrow ; probably acting there in concert with the other cilia in the introduction 

 of food into the mouth. The fourth and last kind of cilia of which I have to speak, consists 

 of two excessively faint, very long, and quite large, bristle-like filaments (si, sf), which project 

 from each end of the body. The straight one (si) always precedes when the creature is in 

 motion, and the curved one (si 1 ) is attached a little to the left of the posterior end of the 

 body. Both are always rigid when the animal is not in motion, — but yet there can be no 

 doubt that they are flexible, for at times they disappear suddenly, and probably are bent 

 under the body. What their office is I cannot say, but conjecture, from their resemblance to 

 what are called the saltatory bristles of other infusorians, that they are used as accessory 

 means of sudden propulsion, or leaping, — a habit which seems to be the most frequent mode 

 of leaving any point at which the creature has fairly come to a stand-still. 



" The contractile vesicle (cv) lies close to the forward end of the body, and corresponds in 

 activity to the vivacity of the motions of the latter. It contracts every ten seconds, and 

 with more vigor than any other that I know of. It is very conspicuous, as it is two thirds 

 of the time in an expanded state ; and disappears and reappears like the sudden closing and 

 opening of a large eye. 



" I have already indicated the position of the mouth (in) as being near the broader, an- 

 terior end of the oblique furrow, but again speak of it here in order to make the description 

 of the digestive system complete. From the mouth (in) the food passes directly into the 

 general cavity without going through any throat, and most frequently combines in large 

 masses (d). 



"The presence of a reproductive organ (n), which we find here in the form of a clear, 

 colorless, globular body, when added to all the other systems which I have mentioned, puts 

 this animal in the condition of a fully organized, ciliated infusorian ; and would seem to give 

 us full warrant for believing it to be the culmination of a progressive development, whose 

 tendency is to pass through such forms of animate organization as we have just been trac- 

 ing in the successively more and more complicated creatures whose images are before us." 



Description of the Figures of Plates IX. and X. 



The corresponding parts in the figures are lettered alike, excepting when otherwise stated in the description ot any 

 particular illustration. 



a a,,,,.;. — b, membranous collar; b 1 , edge of b; b 2 , base of b. — bk, the beaks of the valve of Dysteria. — c, 

 calyx ; c\ aperture of c ; c 2 , lower half of c. — cl, cl\ vibratile cilia. — cv, contractile vesicle. — d, digestive vacuole, 



