174 BULLETIN OF THE 



Staining with picrocarminate of lithium has the advantage of saving 

 time, since it acts rapidly, — the older specimens requiring only one or 

 two hours, the younger from half an hour to an hour. A few grains of 

 picric acid may be added to the dehydrating alcohols which follow the 

 stain, in order to prevent the total extraction of the picric acid, and the 

 consequent disappearance of the yellow color from the nerve fibres. If 

 the object is too deeply stained, the differentiation of nerve tissue does 

 not show well ; the nerve fibres ought to be yellow, the surrounding 

 nuclei pinkish red with a yellow tinge, and all the other tissue pinkish 

 red. As this and Czoker's cochineal are both aqueous dyes, the chromic 

 material is apt to macerate in them ; neither does it stain so well in 

 them as in alcoholic borax-carmine. 



The chloroform method of embedding in parafine was used exclusively. 

 When the embryo has been transferred by the well known method to a 

 vial containing chloroform, the vial should be placed uncorked on the 

 water-bath at 55° to 60° C. Pendent spoons in the large cups are not 

 very serviceable, as the least jar sends the objects off, and it is almost 

 impossible to recover them from the bottom of the cup without injury. 

 It- is better to have ready on the bath an empty warm glass dish, — a 

 common salt-cellar is very good ; also one filled with parafine which 

 melts at about 52° C. The embryos are to be left in the chloroform 

 only as long a time as is necessary for them to sink, and are then to be 

 transferred with the chloroform to the empty glass dish. The transfer 

 is best made by means of a warm pipette, if the embryos are small. 

 Cold soft parafine is then added, a small piece at a time, until the 

 chloroform has so thoroughly evaporated as to leave no trace of its odor. 

 After remaining for fifteen minutes in the soft parafine, the embryo is 

 to be transferred to the " harder" parafine (52° C), where it should 

 remain from fifteen to thirty minutes. It is important to handle the 

 object with great care, and to carry it through the period of heating as 

 quickly as may be ; the latter is necessary, because the embryos are 

 very apt to become brittle if subjected to the heat too long. They 

 should be embedded within an hour or an hour and a half from the 

 time they are first put upon the bath in the chloroform. It is espe- 

 cially dangerous to allow the parafine to harden about the embryo be- 

 fore the latter is finally embedded, because upon the remelting of the 

 parafine the object is almost certain to fall into fragments, owing to its 

 great delicacy. 



The embedding, especially for the younger stages, must be done un- 

 der a lens. It is most convenient to use a dissecting microscope, the 



