Appendix I.— PREPARATION OF THE EGGS. 



The eggs of the lobster may be easily prepared for the study of the external surface 

 in the following way : The fresh eggs are to be placed in either fresh or salt water, which 

 is heated to near the boiling point, until the green pigment coloring the yolk is perma- 

 nently converted into bright red lipochrome (see p. 137). They should then be trans- 

 ferred to cold water and shelled under the dissecting microscope. The eggshell when 

 distended slightly with water may be removed by means of very fine-pointed forceps, 

 nipping the shell and holding it with one pair of forceps while the shell is ruptured 

 and the egg carefully released with the other pair. 



There are two periods in the course of development when it is difficult to remove 

 the shell without injury to the embryo. These are at the close of segmentation, when 

 the blastoderm secretes a fine membrane, which becomes soldered to the shell so that 

 when the latter is removed the blastoderm itself is torn away; and, secondly, either 

 during the egg-nauplius stage or shortly after it. In the early egg-nauplius two 

 membranes can be removed, an outer thick one, the eggshell (composed of the primary 

 and secondary egg membranes), and an inner cuticle, the secreted product of the 

 embryo. This last usually sticks to the tips of the antenna?, the second pair in par- 

 ticular, and carries them with it when it is removed. It sometimes happens that the 

 entire embryo is thus stripped off. 



After shelling, the eggs should be placed at once in Mayer's concentrated picro- 

 sulphuric acid, and left from two to three hours. They may be then transferred to 

 70 per cent and finally to 80 per cent alcohol, aud the latter should of course be 

 changed until all trace of the yellow salt is removed. 



I have frequently made use of 70 per cent alcohol instead of water in making up 

 the picro-sulphuric acid solution, and it is usually successful. I used it with excellent 

 results ten years ago in studying the eggs of Alpheus, but the aqueous solution is 

 perhaps better on the whole. I have tried a great variety of killing and fixing 

 reagents, but none are to be compared for reliability with picro-sulphuric acid in the 

 concentrated form. 



The eggs are stained by placing them in a vial of borax- carmine for the space of 

 two to three minutes or longer, just long enough to stain the surface cells only. The 

 diffuse stain must then be thoroughly removed by acidulated alcohol until the eggs 

 have a light-yellow color, the nuclei of surface cells only being stained red. Turpen- 

 tine is one of the best clearing reagents, none of the essential oils in common use — oil 

 of cloves, origanum, thyme, or bergamot — offering any appreciable advantage over it. 



Clearing requires but a few minutes, and while it is in progress the eggs should 

 be placed in a solid watch glass with turpentine, and examined under a dissecting 

 microscope. With a very small and thin knife they may be cut into halves in any 

 desired plane. It is better to roll the egg under the knife edge, and thus cut into the 

 surface all the way round before pressing the knife through the egg. The eggs cut 

 like cheese at first, but later become brittle and are very apt to break if left in tur- 

 pentine for too long a time. It is thus best to place a few at a time in the clearing 

 fluid, aud cut them at once. 



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