260 Prof. H. James-Clark on the Spongiffi ciliatae 



ntuni, or Podophrya ; and, as counter to what we see in these 

 last, I would state that there are certain of the Vorticellians, 

 closely related to Ejnstylis^ which have no stem whatever, and 

 swim about as freely as Dysteriay 



§ 16. Pleueonema, Duj. 

 Pleuronema instabile^, Jas.-Clk. PI. VII. figs. 75, 76. 



This infusorian bears such a strong resemblance to Hetero- 

 mastix (§ 14) in some of its external features, that it seems as 

 if it might more properly have succeeded the latter in the 

 illustration of my subject ; but mere resemblances do not al- 

 ways indicate relationship : and in the case of Pleuronema^ in 

 particular, this is most true ; for it is decidedly a far more 

 highly organized animalcule than Dysteria^ as we shall see by 

 what I shall now quote from an already published descrip- 

 tion t : — 



" What I wish now to show in the Pleuronema is the triple, 

 or, I might say, even the quadruple diversity of the vibrating 

 cilia, or, in other words, a quadruple specialization of one type 

 of organs, by their manifold offices ranking their possessors 

 above those of their class which attain to a less degree of 

 complexity in this respect. The most prominent of these cilia 

 are those (fig. 75, cT^) which are arranged in longitudinal rows 

 over nearly the whole extent of the body, and which most fre- 

 quently are seen in a quiet state, projecting far out 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 (c?), 

 which project from the oblique fiu'row in which the mouth [m) 

 is set. They are more particularly devoted to producing cur- 

 rents 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 anterior edge of the mouth (??*), 

 one of those proboscis-like lashes {jl) [a flagellimi\ 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 Avere 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 



* See 'Mind in Nature,' ut sujv. p. 148, tig. 00. f See note *. 



