172 



LOWER VERTEBRATES. 



The remarkable family of cave-fishes (Amblyopsid^), is closely allied to the 

 CyprinodontidsB, differing among other things in the position of the vent, which is at 

 the throat, instead of at the usual position behind the ventral fins. The mouth is 

 larger than in the Cyprinodontidae, and the upper jaw is scarcely protractile. The 

 species are viviparous, the young Amhlyopsis having at birth a length of one fourth of 

 an inch. Other peculiarities of the members of the family are rather of the nature of 

 adajstations for their peculiar mode of life. 



The five species known are all small fishes, the largest not exceeding five inches in 

 length. They inhabit the cave streams of Illinois, Indiana, Kentucky, Tennessee, and 

 Alabama, and a single species is found in the ditches in the South Carolina rice-fields. 



Two of the species (Antblyopsis spelceus, Typhlichthys sicbterraneus) inhabit only 

 the depths of the subterranean rivers. In these species, the eyes are reduced to a 



Fig. 106. — Amhbjopsis spekcus, blind fisli. 



useless rudiment, hidden under the skin, the body is translucent and colorless, and the 

 head and body are covered with numerous rows of sensitive pajiilte, which form a 

 very delicate organ of touch. 



In the genus Chologaster, the eyes are ^vell developed and the body colored as in 

 ordinary fishes. In one species ( Cholofjaster picqnlUfer) tactile papillae are developed, 

 as in Amblyopsis. This species lives in cave sjirings of southern Illinois. In the 

 other species there are no tactile papillae. Of these species, one {C. agassizi) was 



taken from a well in Tennessee ; the other ( C. coniutus) 

 is not a subterranean fish at all, being known, as above 

 stated, from the rice ditches of South Carolina. Only the 

 Mammoth Cave blind fish {Amblyopsis spelceus) is as yet 

 common in collections, the others being comparatively 

 rare. It is probable that other species will be found when 

 the lowland swamps and cave streams of the south and 

 west are more fully explored. 



The origin of the blind-fishes is a source of interest- 

 ing speculations. We can hardly resist the conclusion 

 that the cave forms are descended from some species of 

 the type of Chologaster cornutus, which inhabits the low- 

 land streams with its allies, the viviparous Cyprinodonts. 

 It is probable that the family M'as once more numerously 

 represented than it is now, and extended itself over a 

 wider range. The differences separating the Amblyop- 

 sidse from the Cyprinodontidaj seem too radical for us to 

 consider the latter as we now know them as the ancestors of the former, but the two 

 groups probably have had, not far back, a common ancestrj'. 



In regard to the peculiar position of the vent in the Amblyopsidse, we may notice 



Fig. 107 Nervous sj'Steiii of Am- 

 blyopsis I c, cerebi'uni ; e, rudi- 

 mentary eye ; o, optic nerve ; ol, 

 olfactory nerve ; opy optic lobes. 



