188 



MEDUSJ5: — INSECTS— CRUSTACEA. 



which is confirmed by Ranke,* are also developed from 

 the supposed special organs of touch. The latter are 

 much more numerous, as many as sixty being developed 



^^^^Si;. 



-t 



Fig. 116.— Ed£;e of a portion of the mantle of Aglaura hemistoma, with a pair of sense- 

 organs (after Hertwig). v, Velum ; k, sense-organ ; ro, layer of nettle cells ; t, 

 tentacle. 



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. 



Among Insects and Crustacea, there are a great 

 number of peculiarly formed skin appendages, for 

 which it is very difficult to suggest any probable 

 function. 



The lower antennao of the male in Gammarus, for 

 instance, bear a very peculiar slipper-shaped organ, 

 situated on a short stalk : this was first mentioned by 



* " Beit, zu der Lehre. von den Uebergangs Sinnesorganen," Zeit. 

 filr Wiss. Zool, 1875. 



