912 SUMMAEY OF CT7REENT RESEARCHES RELATING TO 



he only occasionally does so. Breeding may be advantageous when 

 pupae can be obtained in a late stage, or when a rare larva is found. 

 But it is extremely difficult to imitate the whole natural conditions for 

 any length of time ; the creature is not strong and vigorous, and 

 though the hairs and setae are less injured, it does not necessarily make 

 a better mount than a hardier well-developed creatm'e born in a 

 natural state, and perhaps caught only a short time after emerging. 

 His o^\-n habit was, therefore, rather to rely upon capture and not 

 breeding. 



Treatment of Pelagic Fish Eggs.* — The transparent eggs of 

 various Telcostei found floating on the surface of the sea present 

 unusual difficulties in the way of hardening. Dr. C. 0. Whitman has 

 had recourse to all the fluids commonly used for this purpose, and 

 failed to find any satisfactory method of hardening the yolk. Even 

 the germinal disk cannot be well preserved by any of the ordinary 

 hardening agents. Kleiuenberg's incro-suli^huric 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 yolk contracts considerably without 

 becoming well hardened even after three days' immersion. 



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

 transferred from the acid to alcohol. The best results have been 

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

 fluid, as used by Dr. Eisig, consists of chromic acid (l-4th per cent.) 

 and platinum chloride (l-4th per cent.) 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 

 before with the same quantity of platinum chloride (l-4th per cent.), 

 everything may be well preserved and hardened except the yolk. 

 Before transferring to alcohol, after one to two days' immersion in 

 this fluid, it is necessary to prick the egg membrane in order that the 

 alcohol may reach the egg readily, otherwise the membrane wrinkles 

 badly and often injures the embryo. 



For the cleavuge stages this fluid cannot be used with success 

 unless the egg has been first killed with another agent, for eggs placed 

 in the 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 

 Dr, Whitman has 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 (one -half per cent,) equal to that of the sea- 

 water is added. After 5-10 minutes the eggs are transferred to the 

 mixture of chromic acid and jilatinum chloride, and left for twenty-four 

 hours or more. This fluid not only arrests the process of blackening, 

 biit actually bleaches the egg. 



After this treatment it is an easy matter to separate the blasto- 

 derm from the yolk by needles, and the preparations thus obtained 



* Amer. Natural., xvii. (1883) pp. 1204-5, 



