PKOBLEMATICAL ORGANS IN LOWER ANIMALS. 187 



the end of the filament, which doubtless proves a very- 

 effective lure.* 



These cases, however, though very interesting, throw 

 little light on the use of the muciferous system 

 in ordinary fish, which, I think, still remains an 

 enigma. 



In some of the lower animals, the nerves terminate 

 on reaching the skin at the base of rod-like structures 

 similar, in many respects, to the rods of the retina, or 

 the auditory rods of the ear, and of which it is very 

 difficult to say whether they are organs of touch or of 

 some higher sense. 



Round the margin of the common sea-anemone is 

 a circle of bright blue spots, or small bladders. If a 

 section be made, there will be found a number of 

 cylindrical organs, each containing a fine thread, and 

 terminating in a " cnidocil (Fig. 14) ; " and, secondly, 

 fibres very like nerve-threads, swelling from time to 

 time with ganglionic expansions, and also terminating 

 in a cnidocil. These structures, in all probability, 

 serve as an organ of sense, but what impressions they 

 convey it is impossible to say. 



Some jelly-fishes (Trachynemadse) have groups of 

 long hairs arranged in pairs at the base of the tentacles 

 (Fig. 116), which have been regarded as organs of 

 touch, and it is certainly difficult to suggest any other 

 function for them. They are obviously sense-hairs, 

 but I see no reason for attributing to them the sense 

 of touch. 



The so-called eyes of the leech, in Leydig's f opinion, 



* Gunther, " Study of Fishes." 



t "Die Augen imd neue Sinnesorgane der Egel.," ReicherVs Arch., 

 18G1. 



