433 l^rof. II. James-Clark on the Structure and 



this beak lies the mouth, to which the former (as frequent ob- 

 servation has proved) acts as a' lip or prehensile organ when food 

 is taken into the body. The prevailing tint is a more or less 

 uniform light gamboge, without the least trace of an eye-spot 

 of any colour. 



A most singular uniformity prevails in the arrangement of 

 the several members of a group. Each monad is attached to its 

 mooring in such a position that its flattened sides lie parallelwise 

 with those of its nearest neighbour ; and the beak projects from 

 that corner of the head which is most distant from the twig. 

 To give a full idea of the peculiarity of this arrangement, it 

 must be stated hei'e that the rigid, arcuate, spasmodically twitch- 

 ing filament mentioned above is attached close to the mouth, 

 and invariably curves away from the beak, and consequently 

 always toward the pedicel of the colony. One is forcibly re- 

 minded by this of the systematic relation of some of the flowers 

 of Labiates, with their stamens projecting far beyond the upper 

 lip of the corolla. The globose heads of the Mentha are particu- 

 larly good examples for illustrating this similitude. 



Prehensile organs. — The only motile organs which this animal- 

 cule possesses are preeminently prehensile in character; and 

 their apparent appropriation to the office of propulsion, when a 

 colony breaks loose from its attachment, I can scarcely doubt is 

 an accidental one, inasmuch as the arcuate cilium continues its 

 spasmodic twitching without any apparent deviation from its 

 usual mode of action. 



There are two cilia, of very unequal size, attached to the trun- 

 cate end of the body. The larger one of these has already 

 been mentioned casually, as a rigid, arcuate filament. It does 

 not taper, but has a uniform thickness from base to tip, and is 

 about half as long again as the body. It arises near the base 

 of the triangular beak, but appears to be separated from the 

 latter by the intervening mouth. When quiet it appears like a 

 bristle, and projects in a line with the longer axis of the body — 

 at the base bending slightly toward the beak, and then sweeping 

 off in a moderate but distinct curve in the opposite direction, so 

 that on the whole it presents a long drawn-out sigmoid flexure. 

 The plane of this curve lies in strict parallelism with the plane 

 of the greater diameter of the body ; iij fact it may be said to be 

 a direct continuation of it. It does not appear to have the cha- 

 racter of a. flagellum, except when assisting the smaller cilium to 

 convey the food to the mouth ; and then it lays aside its rigid 

 deportment and assumes all the flexibility and wavy vibration 

 of the prehensile organ of an Astasia. 



The smaller cilium is an excessively faint body, and almost 

 defies the detective powers of the highest objectives. This is 



