44 A REVISION <>F THE ASTACID^E. 



So it would seem that the blind species sometimes finds its way out from 

 the cave. 



The blind fishes of the Mammoth Cave are compensated for the loss of 

 sight by the development of special tactile papillae. Among the Crustacea 

 the eyeless Gammarus pnteanus and Asettus cavaticus are more richly furnished 

 with olfactory setae than are their relatives that enjoy the sense of sight. 

 In the Astacidae the setae to which Leydig has ascribed an olfactory function 

 are borne by the outer flagellum of the antennules. Le}-dig * has described 

 their arrangement in G. pellucidus. The outer flagellum is composed of about 

 thirty-six segments. The olfactory setae are situate for the most part on the 

 distal half of the flagellum, beginning with the fifteenth segment, the number 

 of setae on each segment decreasing toward either extremity of the olfactory 

 portion of the flagellum. Leydig was unable to compare C. pellucidus with 

 any of the species of Cambarus possessed of eyes, but he observed that the 

 antennulary flagella of Antaeus fliiviatiMs were shorter and contained fewer 

 segments than in ( '. pellucidus. This, however, is a generic distinction, and 

 cannot be brought into relation with the absence of visual organs in the 

 cave species. 



Professor R. Ramsay Wright t has followed up Leydig's suggestion by a 

 comparison of the so-called olfactory organs of C. pellucidus with those of the 

 eyed Gpropinguus. He finds that the external flagellum of the antennule 

 of the latter species is composed of eighteen or nineteen segments, the distal 

 nine of which alone bear olfactory setse. He therefore concludes that 

 C. pellucidus, like the blind Gammarus and Asellus. has acquired a more com- 

 plete olfactory apparatus in compensation for the loss of sight. 



I have examined several specimens of G. propinquus with reference to 

 this point, and find that the number of segments in the external flagel- 

 lum of the antennule may be as high as thirty-live, fifteen or sixteen of 

 which may carry olfactory organs. In C. affinis I have counted as many as 

 thirty-three segments in the flagellum, nineteen with olfactory setae. A 

 moderate-sized ('. Blmidingii from New Jersey reveals about fifty segments, 

 twenty-nine of I hem provided with olfactory setae. It thus appears that 

 Professor Wright's conclusion, that the number of antennulary segments and 

 olfactory organs is increased in the blind species, is not supported by the facts. 

 It is noteworthy, however, that the olfactory setae of G. pellucidus are longer 



• I Litersuchungei] gur Anatoinie und Histologic tin- Tlviere, p. -I s 

 •(■ American Naturalist, Vol Will p. 272, Marcli, LS84 



