ANIMAL METAMORPHOSIS. 177 



the posterior part is prolonged into two elongated spines. It is 

 also furnished with organs of vision. After going through a series 

 of moultings, it comes to present a form which reminds us 

 strongly of a Daphnia (Fig. 27); it is now quite translucent, the 

 body being enclosed in a shield composed of two valves, which 

 are united by a hinge along the upper part of the back, while they 

 are free along their lower margin, where they separate for the 

 protrusion of a large and strong anterior pair of prehensile limbs, 

 provided with an adhesive sucker and hooks, and of six posterior 

 legs adapted for swimming. The bivalve shell is subsequently 

 thrown off, and, forming a broad disc of attachment, the Balanus 

 fastens itself to a rock, and assumes a perfectly fixed and 

 immobile state of existence. The eyes and antennae vanish ; the 

 body is enclosed in a limpet-shaped shell, composed of several 

 pieces, having an aperture in the summit which is closed by a 

 moveable lid, and from which the animal can protrude its delicate 

 legs, or " cirri," which look like a glass hand, and are constantly 

 employed in sweeping the water in search of food, so that it has 

 been compared by an eminent naturalist to a man standing on his 

 head and kicking his food into his mouth. The barnacles (Fig. 

 26) attach themselves to a floating piece of timber^ a ship's 

 bottom, the skin of a whale, or, in some species, to the abdomen 

 of a crab, the anterior portion becoming extremely elongated into 

 the peduncle of attachment. 



The true spiders pass through no metamorphosis, the young 

 being hatched in the form of the parent, but moulting repeatedly 

 before they attain the size of the adult. Their cousins, the mites, 

 however, live a double life. Commencing with only six legs, and 

 then hiding themselves in some crack in the ground, they lie 

 motionless for many days, and ultimately come out with eight legs 

 like minute spiders, but distinguished from them by the fact that 

 their body is always one undivided piece, and not pedunculated ; 

 that is, jointed to the abdomen by a narrow point of attachment. 



It is among the Insects that we find the best-known and most 

 complete series of changes known under the name of metamor- 

 phosis. Born in one shape, the insect dies in another; organism, 

 functions, and habits, all change, the adult insect differing so 

 widely from the young that we cannot in the least recognise the 



