Euphausiidæ. 7 



of 65% alcohol with l /2 — l°/o muriatic acid, by the aid of 

 which the superfluous colour is extracted. The time during which 

 the ova should remain in this solution must be controlled 

 under the microscope. When the best effect is obtained, 

 they should be transferred to 96°/ alcohol, and thence to 

 absolute alcohol, in which they may remain for some time. 

 They can then be cleared up by being transferred to oil of 

 cloves; but in doing this, great care must be employed, as 

 the ova are very apt to shrink when suddenly coming in 

 contact with the oil. Several intermediate solutions of the 

 oil with absolute alcohol ought therefore to be used. In- 

 stead of transferring them successively from the one to the 

 other of these solutions, which is a rather lengthy and 

 troublesome proceeding, I have preferred to use only a 

 single such solution (half oil of cloves, half absolute alcohol) 

 in the following manner. The ova are placed in a small 

 quantity of absolute alcohol in a watch-glass. A drop of 

 the solution is then poured off into the alcohol, and, being 

 heavier than the latter, it will sink to the bottom, whereas 

 the alcohol together with the ova will at first float above 

 it. Gradually, however, the two fluids will mingle, and 

 in sinking down the ova will pass through all degrees 

 of mixture. When the 2 fluids have thoroughly mingled 

 some new drops of the solution may be poured in, 

 whereby the fluid gradually assumes a more concentrated 

 character, approaching that of the above-named solution, 

 into which the ova may now be transferred without any 

 risk. Pure oil of cloves has then gradually to be ming- 

 led with the solution in the same manner as above, and, this 

 being done to a sufficient extent, the ova, or more properly 



