INCUBATION. 95 



from this time the growth of the fish is rapid. 

 At the temperature of 50 the eggs hatch in from 

 forty-five to fifty days this period is lengthened 

 by a lower, and accelerated by a higher tempera- 

 ture. 



A short time previous to hatching, the investing 

 membrane of the egg becomes yellowish-brown 

 in color, and a floss-like coating envelops it, re- 

 minding one by its appearance of the much- 

 dreaded byssus. The movements of the fish, 

 which may have been noted as early as the 

 thirtieth day, become more and more rapid. The 

 previously noticed movements were gentle mo- 

 tions of the tail, but now the whole body seems 

 violently convulsed. At length, with a violent 

 effort, the shell is broken, and the little fish is 

 born. What part first appears to the external 

 world is a matter of perfect indifference. We well 

 remember the consternation of one of our custom- 

 ers on the occasion of a whole tray of eggs hatch- 

 ing tail foremost, when the only work on fish cul- 

 ture in his possession, and in which he had placed 

 the most implicit confidence, declared that the 

 head invariably appeared first. By concentrating 

 upon the mature egg the sun' s rays, by means of 

 a lens, the birth may be hastened, and the efforts 

 of the fish, by which the shell is ruptured, plainly 

 seen. This can only be done as an experiment, as 



