192 



BLIND VERTEBRATES AND THEIR EYES. 



Cuba and of Indiana seems due to the difference in the thickness of the soil, which, 

 as stated, is extremely thin in this part of Cuba. In the manigua frequent fissures 

 or narrow wells lead down to the groundwater. 



There are, finally, the so-called "caves" which also lead down to groundwater. 



As stated above, the caves at Alacranes are of essentially the same character 

 as those of the Carboneria. There are several of these. I have visited three, but 

 obtained fishes from only two, the "M" and Donkey. 



Into the deeper parts of one of the caves visited, the Pedregales, light does not 

 penetrate ; stalactites and stalagmites are clear, tinted rosy, and pure in tone when 

 struck. The usual pool of water did not contain any fish at the time of our visit. 

 An amusing incident occurred at this place. Our guide evidently thought our chief 

 object was to view the marvels of cave formations. When we asked whether there 

 were any caves in the neighborhood with fishes in them, he remarked, "Yes, but 

 the fish don't amount to anything, they haven't any eyes." 



The "M" cave consists, first, of the slight depression in the general surface, 

 and second, of the opening at one side of the depression leading down to the water. 

 The slope is here gentle enough for a zigzag path in the shape of the letter " M " and 

 enables cattle to get to the water at a vertical depth of 83 feet- Light penetrates this 

 cave, and indeed the part directly down from the opening is well lighted. The pool 



Fig. 68a. _ Diagram of the Kentucky Cave RegioD, after Shaler. .4. Sandstone and limestone showing ordinary topography. 

 B. Sink holes. C Domes below large sink holes. D. Upper line of caverns first formed. E. Lower line of caverns. 

 F. Cavern filled with stalactite. G. Lowest line of caverns filled with water. H. Masses of pebbles. 



of water leads off to the left, so that the remote part of the pool is in perpetual dark- 

 ness. This condition makes this cave an ideal place to observe the reaction of the 

 blind fishes to light. As in the Cave of the Insurrectos the caves extend down for 

 an undetermined distance below the surface of the water and blind fish could fre- 

 quently be observed here far below the reach of our io-foot dip net. 



The Donkey Cave is similar to the "M" Cave, but the descent is steeper and 

 there is a large shallow expanse of water on the left of the shaft of light from the 

 opening. The depression at the mouth of the cave is here 9 feet below the general 

 surface and the water is reached at 64 feet below the surface. Water was formerly 

 pumped from this cave for purposes of irrigation. 



The caves about Canas differ from those of the Carboneria and Alacranes. 

 They are cistern-shaped sink-holes rather than caves in the ordinary sense of the 

 word, but on account of the absence of soil there are no funnel-like depressions on 

 the surface to indicate their presence. There is absolutely no general surface indi- 

 cation that one is in a cave country in traveling through it, and it is not until 

 standing at the very brink of one that the presence of a "cave" may be suspected. 

 All of the caves in the Cahas region are modifications of the Modesta type. They 

 are dome-shaped rooms (fig. 69) whose roofs are in different stages of dilapidation 

 and collapse. They have a circular doughnut or crescent-shaped pool of water 



