THE EYES OF THE BLIND VERTEBRATES OF NORTH AMERICA. 171 



eggs were taken was March 8, the latest date May 4. For reasons given in the paper 

 quoted, it is probable that the spawning season extends through the year, but during 

 March the spawning season is evidently at its beginning, and it is during this 

 month and April and May that the early stages may be looked for with the greatest 

 confidence. 



IV. METHODS. 



The usual gamut of killing and fixing reagents was used in preserving the material, 

 chief among which were Perenyi's fluid, Flemming's fluid, Hermann's fluid, vom 

 Rath's fluid, and various mixtures of formalin and corrosive sublimate. Series of 

 sketches and measurements were made on living larvae and embryos. Surface 

 preparations and sections were made of the various stages. 



No eggs were deposited in the laboratory. Females with eggs in the gill-cavities 

 had to be sought for in the caves. When one containing favorable stages was captured 

 she was isolated in a small aquarium and the number of eggs needed freed from 

 the gill-cavity by gently raising the edge of the operculum. The rest of the eggs 

 were permitted to remain in their natural surroundings until another lot was wanted. 

 During the early stages of development the edges of the operculum are closely pressed 

 to the neck and there is no danger of freeing more eggs than are wanted unless the 

 fish is roughly handled. During the later stages of development the tension of the 

 operculum is relaxed and eggs or larva? can be much more easily removed, but there 

 is a correspondingly greater danger of liberating more young than are wanted. If the 

 female is disturbed or confined during the latest stages of brooding, some or all of 

 the young will escape. The eggs freed from the gill-cavity will continue their devel- 

 opment uninterruptedly, but the gill-cavity of the female offers such a unique and 

 self -regulated hatchery that they were usually left in it. 



V. THE EGG AND GENERAL DEVELOPMENT. 



The eggs are large, measuring 2.3 millimetres in diameter. The yolk is trans- 

 lucent, of various tints of amber. The yolk measures 2 millimetres in diameter and 

 contains a large oil-sphere 1 to 1.2 millimetres in diameter. When the egg is deposited 

 the yolk is flabby and composed of yolk-spheres of various sizes loosely put together. 

 After the egg has been in water for some time, the yolk forms a tense rounded mass. 

 The egg is heavier than water. The oil-sphere lies uppermost in the egg, and the 

 germinal disk forms at the side of the egg. Attempts at artificial fertilization have 

 not been successful beyond obtaining well-developed germinal disks. 



