CHAPTER IV 



THE EGGS AND LARV.E AND THEIR DEVELOPMENT 



It follows from the description of their formation, given in 

 the preceding chapter, that the large egg of a dog-fish or skate 

 consists, like a hen's egg, of three parts, the shell, the white, and 

 the yolk. The shell differs from that of the bird's egg in shape 

 colour, and substance. In shape it is somewhat oblong with a 

 tendril or a straight horn at each corner. Fig. 38 shows the shape 



Fig. 38. — Egg of the Larger Spotted Dog-fish, or Nurse-hound ; after Day. 



of the egg of the larger spotted dog -fish ; the eggs of the skates 

 and rays have horns instead of tendrils, and are broader in 

 proportion to their length. The colour is from light brown to 

 black, deepening gradually after the eggs are laid. The sub- 

 stance of the shell is tough, fibrous, and flexible, and contains 

 no lime, the presence of which in large proportion causes the 

 shell of the bird's egg to be hard and brittle. The white, as 

 in the bird's egg, is a thick transparent liquid. The yolk con- 

 tains the essential part of the egg, namely a spot of living 

 substance on its surface which is the germ. No distinct 

 membrane appears to exist on the surface of the yolk. The 

 yolk itself is yellow in colour, of a semi-liquid character, but 

 made up of minute drops. 



