136 THE EOTIFEEA. 



in many loops and curves, and occasionally forming a plexus of complicated inter- 

 twinings. Attached to the canals by long stalks are the little flickering bodies called 

 vibratile tags. The canals are generally visible just under the head, near a plexus, and 

 run down each side of the body, from one plexus to another, till they reach the surface 

 of the contractile vesicle. There are usually five vibratile tags on a side, and a plexus 

 is a favourite point of attachment. 



4. The tags are of various shapes. In some they seem to be simple cylinders, or 

 cones with their bases at the free end. In others they are somewhat wedge-shaped ; so 

 that they have a broad triangular surface from one point of view, and a narrow spindle- 

 shaped surface from another. If a tag happens to point straight up the microscope, a 

 full view may be obtained of "its free end ; and the outlines, so obtained, of these free 

 ends, vary considerably : in the case of Euchlanis dilatata it is a narrow oval with pro- 

 longed pointed ends ; l and in that of Brachionus pala, 2 only a fine straight edge. When- 

 ever I have obtained a distinct edgewise view of a tag, it has had the appearance 

 of being closed at its free end with a knob. Down the length of the tag (when so seen) 

 run an endless succession of swift undulations ; which, on several occasions, in the 

 dying animal, I have seen slowly slacken, till they have gradually resolved themselves 

 into what seemed to be one stout, tapering, undulating cilium, of the length of the tag 

 itself, attached by its broad base to the knob mentioned above, and pointing its taper 

 extremity to the lateral canal. 



But when the tag presents its broad triangular surface to the observer, there is a 

 totally different appearance ; and it seems to be crossed by quivering, parallel, straight 

 lines that stretch from one side to the other (PI. XIII. fig. 8Z>). It is obvious that no 

 single cilium could present such an appearance. Possibly an undulating membrane 

 might, the cross-lines being the summits of the waves which happened to be in focus ; 

 but the lines seem to be too sharp for this. Dr. Moxon suggests that the cross-lines are 

 produced by rows of extremely minute cilia on each inner broad surface of the tag. It 

 is not easy to imagine what such an apparatus might look like when seen in motion 

 sidewise ; but possibly the apparent waves produced by the cilia on either side might 

 together cause the illusory appearance of an undulating cilium as long as the vibratile 

 tag. That many of the inner surfaces of the Botifera are lined with minute cilia has 

 long been known. The whole alimentary tract is so ; and, what is more to the point, 

 this very appearance of a long undulating cilium is certainly produced in the tube of 

 Floscularia campanulata by very minute cilia running in straight lines down its length. 3 



5. The next point is whether these tags are open or closed at their free ends. On 

 this point it is enough to say that direct observation has entirely failed to decide the 

 question. The chief authorities have come to opposite conclusions, and there seems to 

 be no hope of settling the point by the microscope. The close analogy between the 

 vibratile tags of the Rotifera and the appendages on the water-vessels of the Naids 

 would, however, lead us to infer that in the former case, as well as in the latter, the 

 tags in spite of appearances may be open funnels, furred inside with minute cilia. A 

 similar difficulty awaits us when we inquire how the lateral canals originate in the 

 head. In some cases the canals on either side are said to have their fore ends on the 

 surface 4 in communication with the free water, in others to cross from side to side and 

 anastomose 5 ; so that the whole apparatus forms a loop with its two ends attached either 

 to the cloaca or to the contractile vesicle ; while in the great majority of cases it is im- 

 possible to say what is the real arrangement. 



6. In attempting to determine the use of this apparatus we are met by this obvious 

 difficulty ; that we are not sure of the facts. Are the vibratile tags open at their free 



1 Dr. Plate (126) Taf. ii. fig. 19, c. 2 C.T.H. vol. ii. p. 117. 



3 PI. D, fig. 1 ; also Dr. Moxon (118). 



4 As observed by Mr. Gosse in Ptcrodina patina and P. valvata, vol. ii. p. 138. 



5 As observed by Professor Huxley in Lacinularia socialis (91) ; by Dr. Leydig in the same (108) ; 

 and by myself in Stcphanoccros Eichhornii, PI, iv. figs. 2, 4. 



