No. 5. — The Eyes in Blind Crayfishes. By G. H. Parker. 1 



In the fall of 1888 Mr. Samuel Garman placed at my disposal several 

 crayfishes 2 which had been collected by Miss Rath Hoppin in the caves 

 of Jasper County, Missouri. The specimens were given to me with the 

 suggestion that I should ascertain the extent to which their eyes had 

 degenerated, for, judging from external appearances, these organs hail 

 become as rudimentary as the eyes of the blind crayfish, Cambarus 

 pellucidus, Tellk., from Mammoth Cave. In order to establish compari- 

 sons it was desirable to study the eyes in C. pellucidus, and for this 

 purpose specimens of this species were kindly furnished me from the 

 collections in the Museum of Comparative Zoology. These specimens, 

 as well as those collected by Miss Hoppin, were preserved in strong- 

 alcohol. My study of this material was carried on in the Zoological 

 Laboratory of the Museum, under the direction of Dr. E. L. Mark. 



Notwithstanding the general interest which zoologists have shown in 

 the blind crayfishes there have been very few publications on the minute 

 structure of the eyes of these animals. The earliest contribution to this 

 subject was from Newport, who, in discussing the ocelli of Anthophora- 

 bia, incidentally described the structure of the eye in Cambarus pellu- 

 cidus. According to Newport's account ('55, p. 164), the eyes in this 

 species would seem to be only partially degenerated, for although the 

 retinal region is not pigmented, the corneal cuticula is nevertheless 

 divided into irregular facets, or " corneales," as they are termed, " and 

 the structure [hypodermis] behind these into chambers to which a small 

 but distinct optic nerve is given." 



The second investigator who studied the eyes of blind crayfishes was 

 Leydig ('83, pp. 36 and 37). The material which was accessible to him 

 was unfortunately so poorly preserved that it was of little value for his- 

 tological purposes. He nevertheless satisfied himself that the cuticula 

 in the corneal region was not facetted. He also quoted from an abstract 



1 Contributions from the Zoological Laboratory of the Museum of Comparative 

 Zoology, under the direction of E. L. Mark, No. XX. 



2 These crayfishes had previously heen submitted to Dr. Walter Faxon for 

 determination. They have since been described by him as a new species, under 

 the name of Cambarus setosus, an account of which will be found in Mr. Garman's 

 recent paper ('89, p. 237) on "Cave Animals from Southwestern Missouri." 



vol. xx. — no. 5. 



