DEVELOPMENT. 
209 
ing its mode of life. In the development of the common 
Crab, so different is the outward form of the newly 
Fig. 178.—Metamorphosis of the Mosquito (Ctilexpipiens) : A, boat of eggs ; B, some 
of the eggs highly magnified; d, with lid open for the escape of the larva, C; D, 
pupa; E, larva magnified, showing respiratory tube, e, anal fins,/, antennae, g; 
F, imago; a, antennae; &, beak. 
hatched embryo from that of the adult, that the former 
has been described as a distinct species. 
The most remarkable example of metamorphosis among 
Vertebrates is furnished by the Amphibians. A Tadpole 
—the larva of the Frog—has a tail, but no legs; gills, in¬ 
stead of lungs; a heart precisely like that of the Fish; a 
horny beak for eating vegetable food, and a spiral intes¬ 
tine to digest it. As it matures, the hinder legs show 
themselves, then the front pair; the beak falls off; the 
tail and gills waste away; lungs are formed; the diges¬ 
tive apparatus is changed to suit an animal diet; the heart 
is altered to the Reptilian type by the addition of another 
auricle; in fact, skin, muscles, nerves, bones, and blood¬ 
vessels vanish, being absorbed atom by atom, and a new 
set is substituted. Moulting , or the periodical renewal of 
epidermal parts, as the shell of the Lobster, the skin of 
14 
