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 toa 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 the 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 
fe) 
