172 LECTURE IX. 



exti'aortlinary diversity is displayed. Not only are tliey stretched 

 under all possible angles from the main stem, at times seeming per- 

 pendicular to it, or bent more or less in the same direction, and again 

 as if combed into one ma?s ; but a moment afterwards every thread 

 seems to be curled or waving, the main thread being straight or 

 undulating, then the shorter threads will be stretched straight for 

 some distance, and then suddenly bent at various angles upon them- 

 selves, and perhaps repeat such zigzags several times, or they will be 

 stretched in one direction, then they will be coiled up from the tip, 

 and remain hanging like pearls, suspended by a delicate thread to 

 the main stem, or, like a broken whip, be bent in an acute angle 

 upon themselves, witli as stiff an appearance as if the whole -were 

 made up of wires ; and, to complete the wonder, a part of the length 

 of the main thread will assume one appearance, and another part 

 another, and pass from one into the other in the quickest possible 

 succession, so that I can truly say I have not known in the animal 

 kingdom an organism exhibiting more sudden changes, and present- 

 ing more diversified and beautiful images, the action, meanwhile, 

 being produced in such a way as hardly to be understood. For, 

 when expanded, these threads resemble rather a delicate fabric spun 

 with the finest spider's thread, at times brought close together, 

 combed in one direction without entangling, next stretched apart, 

 and preserving in this evolution the most perfect parallelism among 

 themselves, and at no time, and under no circumstances, confusing 

 the fringes of the two threads. They may cross each other, they 

 may be apparently entangled throughout their length, but let the 

 animal suddenly contract, and all these innumerable interwoven 

 fringes inifold, contract, and disappear, reduced, as it were, to one 

 little drop of most elastic India rubber." * 



If we regard with Agassiz the halves of the body of the Beroe, 

 which might be divided by a plane passing through the split of the 

 oblong mouth, as " right " and " left," the tentacles are there placed 

 one on the right, and the other on the left, side of the animal. 



The transverse mouth, situated in Ci/dippe at the extremity marked 

 a, fig. 77., is bounded in most ciliogrades by lobes, and the buccal 

 membrane in some species is produced into minute and highly con- 

 tractile tentacles. Below these the alimentary canal expands into a 

 moderately wide stomach extending about half-way towards the 

 opposite pole. The form of the cavity varies according to its state of 

 contraction, from circular to oblong or angular. Towards the fundus 



* This beautiful description is given by Agassiz, in his vahiablc and clabcratc 

 monograph, CXLVUI. pp. 314, 315. 



