44 A-REVISION OF THE ASTACIDA. 
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 papilla. Among the Crustacea 
the eyeless Gammarus puteanus and Asellus cavaticus ave more richly furnished 
with olfactory sets than are their relatives that enjoy the sense of sight. 
In the Astacidx -the setee to which Leydig has ascribed an olfactory function 
are borne by the outer flagellum of the antennules. Leydig * has described 
their arrangement in C. pellucidus. The outer flagellum is composed of about 
thirty-six segments. The olfactory sete are situate for the most part on the 
distal half of the flagellum, beginning with the fifteenth segment, the number 
of setz on each segment decreasing toward either extremity of the olfactory 
portion of the flagellum. Leydig was unable to compare C. pel/ucidus with 
any of the species of Cambarus possessed of eyes, but he observed that the 
antennulary flagella of Astucus fluviatilis were shorter and contained fewer 
segments than in C. 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 C. propinquus. He finds that the external flagellum of the antennule 
of the latter species is composed of eighteen or nineteen sezments, the distal 
nine of which alone bear olfactory sete. 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 C. 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-five, fifteen or sixteen of 
which may carry olfactory organs. In C. ufinis I have counted as many as 
thirty-three segments in the flagellum, nineteen with olfactory seta. A 
moderate-sized C. Blandingii from New Jersey reveals about fifty segments, 
twenty-nine of them provided with olfactory sete. 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 sete of C. pellucidus are longer 
* Untersuchungen zur Anatomie und Histologie der Thiere, p. 38. 
+ American Naturalist, Vol. XVIII p. 272, Mareh, 1884. 
