104 THE POPULAR SCIENCE MONTHLY. 



In some of the lower animals the nerves terminate on reach- 

 ing 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 



Fig. ^.— Ceratius bispinosus ("Challenger Reports," vol. xxvii). 



will be found a number of cylindrical organs, each containing a 

 fine thread, and terminating in a " cnidocil " ; and, secondly, fibers 

 very like nerve-threads, swelling from time to time with gangli- 

 onic expansions, and also terminating in a cnidocil. These struct- 

 ures, in all probability, serve as an organ of sense, but what 

 impressions they convey it is impossible to say. 



Some jelly-fishes (Trachynemadce) have groups of long hairs 

 arranged in pairs at the base of the tentacles (Fig. 3), 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 them to the sense of 

 touch. 



The so-called eyes of the leech, in Leydig's * opinion, which is 

 confirmed by Ranke,f are also developed from the supposed special 

 organs of touch. The latter are much more numerous, as many 

 as sixty being developed on the head alone. They are cylindrical 

 organs, lined with large nucleated refractive cells, which occupy 

 nearly all the interior. A special nerve penetrates each, and, 

 after passing some way up, appears to terminate in a free end. 



I may also allude to the very varied bristles and cirrhi of 

 worms, with their great diversity of forms. 



* " Die Augen und neue Sinnesorgane dcr Egel," " Reichert's Arch.," 1861. 

 f " Beit, zu der Lehre von den Uebergangs-Sinnesorganen," " Zeit. f iir wiss. Zool.," 

 1875. 



