614 EEPORT OF COMMISSIONER OF FISH AND FISHERIES. [8] 



figures and astei-s developed in eggs during their early stages of devel- 

 opment. For this purpose he uses solutions of chromic acid of one-tenth 

 of 1 per cent, to one-half of 1 per cent. 



Dr. Whitman has recently discussed its unsuitableness when used 

 alone in the treatment of pelagic fish -eggs in the American Naturalist 

 for November, 1883. He writes: "The transparent eggs of various 

 Teleostei floating on the surface of the sea x^resent unnsual difficulties 

 in the way of hardening. I have had recourse to all the fluids commonly 

 used for this purpose, and have failed to find any satisfactory method 

 of hardening the yelk. Even the germinal disk cannot be well pre- 

 served by any of the ordinary hardening agents. Kleinenberg's picro- 

 sulphuric acid, for instance, causes the cells all through the cleavage 

 stages as well as the later embryonic stages to swell, and in many cases 

 to become completely disorganized. The embryonic stages can be 

 hardened in chromic acid (1 per cent.), but the yelk contracts consider- 

 ably without becoming well hardened even after three days' immer- 

 sion. 



"All sorts of wrinkles and distortions are caused when the ova are 

 transferred from the acid to the alcohol ; my best results have been ob- 

 tained with osmic acid and a modified form of Merkel's fluid. This 

 fluid, as used by Dr. Eisig, consists of chromic acid (one-fourth per 

 cent.) and platinum chloride (one-fourth percent.), mixed in equal parts. 

 Thus prepared it causes maceration of the embryonic portion of the egg. 

 By using a stronger chromic acid (1 per cent.), and combining it as be- 

 fore with the same quantity of platinum chloride (one-fourth per cent.), 

 everything may be well preserved and hardened except the yelk. Before 

 transferring to alcohol, after one to two days' immersion in this fluid, 

 it is necessary to prick the agg membrane in order that the alcohol may 

 reach the Qgg readily, otherwise the membrane wrinkles badly and often 

 injures the embryo. 



" For the cleavage stages this fluid cannot be used with success un- 

 less the egg has been first killed by another agent; for eggs placed in 

 this fluid continue to live for a considerable time, and may even pass 

 through one or two stages of cleavage. It is therefore necessary to use 

 some agent that kills almost instantly. For this purpose, I have found 

 osmic acid the best reagent. The eggs are placed in a watch-glass with 

 a few drops of sea- water, and then a quantity of osmic acid [^ per cent.)^ 

 equal to that of the sea-water, is added. After five to ten minutes the 

 eggs are transferred to the mixture of chromic acid and platinum chlo- 

 ride, and left for twenty-four hours or more. This fluid not only arrests 

 the process of blackening, but actually bleaches the e,gg. 



"After this treatment it is an easy matter to separate the blastoderm 

 from the yelk by needles, and the preparations thus obtained can be 

 mounted in toto or sectioned. As the blastoderm is quite thin during 

 the cleavage stages, a whole series of these stages may be mounted and 

 studied from the surface to advantage. After removal from the acid the 



