How to obtain it. 193 



very disturbing to them, and the box lids should be kept closed 

 except at the ends. The front end of a lid should be placed on 

 the water board or breakwater at the head of the box. This will 

 prevent any light getting in from that direction. My lids are half 

 the length of the boxes, that is two lids to a box. By removing 

 the lower lid, therefore, that half of the box is exposed to the light, 

 and the alevins soon desert it, and they push their way up to 

 the darkness, and it will be seen that the darkest portion of the 

 upper half of a semi-covered box is that part which lies a little 

 behind the water board. Here the alevins are not only out of 

 the light, but they are also in the place of all others where the 

 currents are best adapted to their requirements. By slightly dis- 

 colouring the water at this point, by means of some harmless 

 ingredient, the currents can be quite easily traced. 



So much, then, for the packing of the "alevins." Let us 

 take another good look at one of them soon after escaping from 

 the shell in which it has been developed. It is possessed of a 

 body having a head in which are placed two large eyes. The 

 mouth is apparent, but requires further development. There is 

 a large transparent looking sac attached to the fish, which contains 

 a number of yellow oil globules, and is covered with a network of 

 veins, and the heart may be seen, showing as a deep red patch of 

 colour which pulsates regularly. By using a microscope, a 

 more interesting sight may be witnessed than in examining an 

 egg, inasmuch as the little creature is now further developed. 

 The heart is to be found well forward of the umbilical sac, or 

 between it and what will be the lower jaw ; it is double, one side 

 of it receiving the blood from the veins, and the other sending it 

 out again to all parts of the body. Two blood vessels will be 

 seen to run the entire length of. the body, and the blood may be 

 seen coursing along within their walls, in the one going towards the 

 heart, and in the other in the opposite direction. One of the 

 main arteries is also to be distinctly traced by the naked eye on 

 the underside of the sac, and the action of the blood may be 

 clearly seen here also. I do not know a much more interesting 

 microscopic sight than that of the circulation of the blood in a 

 young fish at this stage of its existence. 



Of the fins the pectorals are the most developed at this 

 o 



