FISH EGGS. 605 



The eggs of birds have a space at their blunt end filled with gas; this 

 gas contains on an average 18.0-19.9 per cent oxygen (HiJFNER). 1 



The weight of a hen's egg varies between 40-60 grams and may some- 

 times reach 70 grams. The shell and shell-membrane together, when 

 carefully cleaned, but still in the moist state, weigh 5-8 grams. The 

 yolk weighs 12-18 and the white 23-34 grams, or about double. The 

 entire egg contains 2.8-7.5, or average 4.6, milligrams of iron oxide, and 

 the quantity of iron can be increased by food rich in iron (HARTUNG 2 ) . 



The white of the egg of cartilaginous and bony fishes contains only traces of 

 true albumin, but consist at least in many fishes, of mucin substance ; and the 

 cover of the frog's egg also consists, according to GIACOSA, of mucin. The eggs 

 of the river-perch contain, HAMMARSTEN 3 claims, mucin in the envelope in the 

 unripe state and only mucinogen in the ripe state. The crystalline formations 

 (yolk-spherules, or dotterplattcheri) which have been observed in the egg of the 

 tortoise, frog, ray, shark, and other fishes, and which are described by VALEN- 

 CIENNES and FREMY under the names emydin, ichthin, ichthidin, and ichthulin, 

 seem, as above stated in connection with ichthulin, to consist chiefly of phos- 

 phoglycoproteins. The klupeovin obtained by HUGOUNENQ 4 from the herring's 

 eggs and from which he obtained the three so-called hexone bases and abundant 

 monamino-acids, especially leucine, but not glycocoll or glutamic acid, is to 

 all appearances not a unit body. The eggs of the river-crab and the lobster 

 contain the same pigment as the shell of the animal. This pigment, called cyano- 

 crystallin, becomes red on boiling in water. 



C. MORNER 5 has isolated a substance which he calls percaglobulin, from the 

 unripe eggs of the river-perch. It is a globulin and has a strong astringent taste. 

 Especially striking is its property of precipitating certain glycoproteins, such as 

 ovomucoid and ovarial mucoids, and polysaccharides, such as glycogen, gum 

 tragacanth and starch-paste, and of being precipitated by them. 



In fossil eggs (of APETNODYTES, PELECANUS, and HALL^US) in old guano 

 deposits, a yellowish white, silky, laminated compound has been found which 

 is called guanovulit, (NH 4 ) 2 SO 4 + 2K 2 SO 4 +3KHSO 4 +4H 2 O, and which is easily 

 soluble in water, but is insoluble in alcohol and ether. 



Those eggs which develop outside of the mother-organism must con- 

 tain all the elements necessary for the young animals. One finds, there- 

 fore, in the yolk and white of the egg an abundant quantity of protein 

 bodies of different kinds, and especially phosphorized proteins in the yolk. 

 Further, we also find abundance of phosphatides in the yolk, which seem 

 to occur habitually in all developing cells. The occurrence of glycogen is 

 doubtful, and the carbohydrates are perhaps represented by a very small 

 amount of sugar and glycoproteins. On the contrary, the egg contains a 

 large proportion of fat, which doubtless is important as a source of supply 

 for nourishment and in maintaining respiration for the embryo. The 



1 Arch, f . (Anat. u.) Physiol., 1892. 



2 Zeitschr. f. Biol. 43. 



3 Giacosa, Zeitschr. f. physiol. Chem., 7; Hammarsten, Skand. Arch. f. Physiol., 17. 



4 Valenciennes and Fremy, cited from Hoppe-Seyler, Physiol. Chem., p. 77; 

 Hugounenq, Bull. soc. chim. (3), 33, and Compt. rend., 143. 



5 Zeitschr. f. physiol. Chem., 40 



