DEVELOPMENT OF THE CHICK EMBRYO. 639 



embryo of the hen. The embryo does not contain any gelatin-forming 

 substance until the tenth day, and from the fourteenth day on it contains 

 a body which, when boiled with water, gives a substance similar to chon- 

 drin. A body similar to mucin occurs in the embryo when about six 

 days old, but then disappears. The quantity of haemoglobin shows a 

 continual increase compared with the weight of the body. LIEBERMANN 

 found that the relation of the haemoglobin to the body weight was 1:728 

 on the eleventh day and 1:421 on the twenty-first day. 



By means of BERTH BLOT'S thermometric methods TANGL l has 

 determined the chemical energy present at the beginning and end of 

 the development of the embryo of the sparrow's and hen's eggs. The 

 difference was considered as work of development. He found that the 

 chemical energy necessary for the development of each gram of ripe hen's 

 embryo (Plymouth) was equal to 0.805 Cal. This energy originated 

 chiefly from the fat. Of the total chemical energy utilized, about 70 

 per cent was used for the embryo and about 30 per cent remained in the 

 yolk. Of the utilized energy about two-thirds was used in the con- 

 struction of the embryo and about one-third transformed into other 

 forms of energy as work of development. 



By their investigations on the development of the trout egg, TANGL 

 and FARKAS 2 have found that the loss in weight of each egg which had 

 an average weight of 88 milligrams was 4.9 milligrams during the 42 

 days of incubation, of which 4.11 milligrams was water and 0.722 milli- 

 gram dry substance with 0.367 milligram C. The eggs lose no nitro- 

 gen and no fat. The fat content increases a little, and indeed, as these 

 authors believe, at the expense of the proteins. The chemical energy 

 used during development was 6.68 gram-calories. 



The highly interesting investigations made by LOEB upon the fer- 

 tilization of the eggs of lower sea-animals will be discussed in this con- 

 nection. According to these experiments after the fertilization of the 

 egg by means of a sort of cytolysis small drops of a colloid substance 

 form on the surface of the egg. These drops enlarge in volume and 

 conglomerate to a continuous mass, while its surface hardens to a tight, 

 continuous membrane the fertilization membrane. The process of 

 membrane formation is in fact the essential step in the fertilization. 

 Besides, by spermatozoa, the membrane formation is caused by different 

 actions. For many eggs all that is necessary is the artificial calling 

 forth of the processes for the membrane formation in order that the 

 egg shall develop to normal larvse (for example the eggs of the star 

 fish and of certain worms) . In other cases, for example the sea-urchin, 

 Strongylocentrotus, a second action is necessary for the production of 



i Pfliiger's Arch., 93 and 121. 2 Ibid., 104. 



