226 THE INFANCY OF ANIMALS 



stalk-eyedness in the case of the hammer-headed shark, 

 but the hkeness here is not very close. 



The Sword-fish in the course of its development from 

 the egg onwards presents some curious changes. Just 

 compare, for a moment, the three figures on the adjoining 

 page, and note, first of all, the differences in the fins. 

 The long, low back fin of the youngest, the semicircular 

 fin of the middle stage, and the high, deep fin of the later 

 growth, which even now has not assumed its fuUy adult 

 form. The pair of fins answering to the hind limbs of 

 higher vertebrates in the youngest specimen have as yet 

 only begun to sprout ; in the second they have enor- 

 mously lengthened, forming two long, slender rods, 

 while in the third stage they have decreased in length. 

 Next, it should be noted that in the youngest specimen 

 the gill-cover bears a long, backwardly directed spine; 

 in the' next stage the spine is longer and more slender, 

 and the gill-cover is larger. At the top of the gill-cover, 

 in both these stages, is another large spine. In the later 

 stage the upper spine has almost vanished and the lower 

 has become extremely reduced. Then it should be 

 noticed, that in the younger stages the jaws are of equal 

 length — the " sword " does not make its appearance till 

 the third stage is reached. Finally, note the great 

 difference in the size of the eye, that of the third stage 

 having decreased considerably — possibly because the 

 earlier days are spent in deeper water than the later stages. 



The young of the Angler {Lophius piscatorius) affords 

 a no less striking series of changes in the course of its 

 growth from the egg to the adult. Look first at the 

 newly hatched fish. Translucent and finless, and bearing 

 a great burden of food in the shape of a yolk-sac, it gives 

 but little forecast of the hideous thing it is going to be. 



