68 



BLIND VERTEBRATES AND THEIR EYES. 



All these gobies are tenacious of life, especially the blind ones. Several of 

 the latter have been kept in a half-gallon jar of water for several weeks without 

 change of water, and others have been kept several months in confinement in my 

 laboratory. When the water becomes somewhat stale, they frequently rise to the 

 surface and use the water as a plane to which' they attach themselves by means 

 of their ventrals. The earliest date at which I procured young was October 25. 

 The smallest caught at that time is represented in figure 26 b. 



The covering of the ovarian egg consists first of a finely striate membrane, the 

 zona radiata of all teleostean eggs. Exterior to this is a network of threads with 

 the meshes coarsest at the entodermic pole and forming almost a continuous mem- 

 brane at the ectodermic pole. When the eggs are deposited, the meshwork of 

 threads is stripped off the egg and remains attached to the zona radiata around 



Fie. 27. Larval Typhlogobius in its membrane. 



the micropyle. In the eggs deposited naturally by the females in confinement 

 the threads were wound together to form a cord at the micropylar end of the egg. 

 The cords of many of these eggs were attached to each other, and the eggs thus came 

 to be laid in bunches like those of grapes. In their natural habitat the eggs are 

 fastened by the threads to the lower surfaces of the rocks under which they live, 

 and the membranes are expanded into long club-shaped bags. The yellow of 

 the blind-fish egg is entirely confined to the yolk, which contains many oil globules. 

 The granular protoplasm is opaque. In females with ripe eggs they are frequently 

 to be seen forming a yellow band along the flanks. 



The eye in the larvse just about to be hatched (fig. 27) is apparently normal. 



The histology of the adult eye was studied by Ritter, who comes to the follow- 

 ing conclusion : 



1. In the smallest examples studied the eyes, though very small, are distinctly visible even in 

 preserved specimens — so distinctly that the lens is plainly seen. In the largest examples, on the 

 other hand, they are so deeply buried in the tissue as to appear even in the living animals as mere 

 black specks, while in preserved ones they are in many cases wholly invisible. 



2. Neither in small nor in large specimens does the epidermis over the eye differ in thickness or 

 structure from that of adjacent regions. In the large individuals the much greater thickness of the 

 tissue here is brought about by an increase in the sub-epidermal connective tissue, the growth of 

 which can be seen taking place in the embryonal connective-tissue cells that are found here. 



3. As is the case with rudimentary organs generally, the eye is subject to great individual varia- 

 tion in size, form, and degree of differentiation. 



4. The only parts of the normal teleostean eye, no traces of which have been found, are the 

 argentea, the lamina suprachoroidea, the processus falciformis, the cones of the retina, the vitreous 

 body proper, the lens capsule, and in one specimen the lens itself. 



5. In the parts present the rudimentary condition of the organ is seen in the very slight develop- 

 ment of the choroid, no cellular elements being present in this excepting in the chorio-capillaris, 

 and here to a quite limited extent, the rest of that layer being composed exclusively of pigment; 



