gill] 



THE UMBRAS 



303 



In li'ke localities the eggs of the Umbra were found by Ryder 

 (1886), "laid singly upon aquatic plants to which they adhere 

 for a time by means of a thin coating of adhesive matter which in- 

 vests them." The eggs are about a millimeter and a half ('1.6 mm.') 

 in diameter. A peculiarity of the fertilized egg is that, at the time 

 of the formation of the blastodisk, " the vitellus displays a most active 

 amoeboid activity of its substance," and Ryder remarked that he 

 knew " of no teleostean egg " in which " such amoeboid movements of 

 the vitellus are so pronounced and rapid." On or about " the sixth 

 day " after oviposition, " the young mud-minnow leaves the egg," 

 and " three days after hatching the air-bladder becomes apparent 

 as a fusiform vesicle behind the pectorals and above the foregut, 

 when the young fish is viewed as a transparent object." Then 

 " pigment is rapidly developed upon the upper and lateral aspects of 

 the body, and by the sixteenth day the larvae have become pretty 

 dark in color, when observed from above." 



Fig. 38. — Western Umbra {Umbra limi). After Jordan and Evermann. 



The mud-minnow is an excellent fish for aquaria, as it will live 

 under conditions which other fishes cannot stand. Some kept in a 

 small jar lived for months without change of water save for that 

 supplied only sufficiently to compensate for what was lost by evapora- 

 tion. The only plants for keeping the water clear were some 

 Oscillariaceous confervae. The fishes would ascend from time to 

 time to the surface and reject bubbles of air (carbonic acid gas) and 

 take in with a gulping action fresh air. Some were kept for about 

 a year by the present writer in a large glass jar; during an unusually 

 cold period the water froze solid and the jar was broken. The lump 

 of ice was allowed to melt gradually and all the fishes revived and 

 swam about as lively as ever in the new receptacle furnished them. 

 A sudden transfer of frozen fish to " temperate " or summer water 

 was found to be injurious or even fatal. 



