172 



LOWER VER TEBRA TES. 



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

 CyprinodontidiE, 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 vi\iparous, the young A»ibli/opsis 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 

 adaptations 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 {Amblyopsis spelceus, TyjyhUchthys subterraneus) inhabit only 

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



Fig. 106. — AmUijopsls sjuheus, blind fish. 



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

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

 very delicate organ of touch. 



In the genus Choloffaster, the eyes are well dcveloiied and the body colored as in 



ordinary fishes. In one species {Chologaster 2MpilIifer) tactile papillae are developed, 



as in Ambli/opsis. This species lives in cave springs of southern Illinois. In the 



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



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



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 (Ambli/opsis 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 prol:)able that the family was once more numerously 

 represented than it is now, and extended itself over a 

 wider range. The differences separating the Amblyop- 

 sidae from the Cyprinodontidae seem too radical for us to 

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

 groups probal)ly have had, not far back, a common ancestry. 



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



Fig. 107.— Nervnus h\stem o£ Aiii 

 bhjo}isis; c, ceiebruiii ; e, rudi 

 nientary eye ; o, optic nerve ; ot 

 olfactory nerve ; op, optic lobes. 



