I EGGS AXD TADPOLES 9 



vent by hundreds ; each is a little globular body about 

 yVth inch in diameter, half black and half white, and 

 surrounded by a sphere of clear jelly, by means of which 

 the eggs adhere together in large irregular masses, the 

 well-known " frog-spawn." As the eggs are laid, the 

 male passes out of his body, also by the vent, a milky 

 spermatic substance or milt, which gets access to the eggs 

 and impregnates or fertilises them. Without impregna- 

 tion they are incapable of developing. 



Neither male nor female takes the slightest care of the 

 eggs when once they are deposited and fertilised. They 

 are simply left in the water unprotected in any way ; and, 

 naturally enough, the mortality among them during the 

 course of development is very great, the majority being 

 eaten or otherwise destroyed, and only a very small per- 

 centage coming to maturity. 



The first noticeable change in the spawn is that the 

 sphere of jelly surrounding each egg swells up so as to 

 acquire several times the diameter of the enclosed egg. 

 The egg itself, or embryo, as it must now be called, 

 gradually becomes entirely black, then elongates, and 

 takes on the form of a little creature (Fig. i, i) with a 

 large head, a short tail, and no limbs ; which after wrig- 

 gling about for a time, escapes from the jelly and fixes 

 itself, by means of a sucker on the underside of its head, 

 to a water-weed. Great numbers of these tadpoles, as the 

 free-living immature young or larvce of the frog are called, 

 may be seen attached in this way. At first they are 

 sluggish and do not feed, but, before long, they begin to 

 swim actively by lashing movements of their tails, and 

 to browse on the weeds. They are thus in the main 

 vegetable-feeders, not carnivorous, like the adult frog. 

 On each side of the head appear three little branched 

 tufts or gills, which serve as respiratory organs (2, 2'), 

 the tadpole, like a fish, breathing air which is dissolved 



