; 9 6 



THE POPULAR SCIENCE MONTHLY. 



requiring no intelligent effort, it may be regarded as the lowest. But 

 even in this there is unbounded variety. We will distinguish the 

 following classes : 



1. Transformed epidermis constitutes the armor of the lobster, in- 

 sects, and hard-skinned articulates in general. Also the hair of mam- 

 mals, the feathers of birds, the scales which cover most fishes, reptiles, 

 and the legs of birds, and the plates of that lizard-like mammal, the 



4gj 



iSmm ^m^Mmm 



Fig. 1. Manis {Manis itentadactylcC). 



manis. 2. Stony secretion of the skin. Here belong the limy shells 

 of mollusks, the tests of sea-urchins, star-fishes, etc. ; also those of the 

 chalk-forming rhizopods, and the silica shells of other microscopic ani- 

 mals. 3. True oony armor produced by the skin ; as the coat-of-mail 

 of the armadillo, and the scale-armor of the ganoid fishes, the bony 

 pike and sturgeon, for example (also the armor of the group to which 



Fig. 2. Stukgeon (Acipenser). 



belong the trunk-fishes. This sort of armor was very common among 

 the most ancient fishes, but it has now gone quite out of fashion. 

 The crocodile and alligator still have this bone armor in great per- 

 fection, and covered with epidermic plates that is, they have a com- 

 bination of 1 and 3. Altogether they are as well protected as any 



Fig. 3. Ostraciontidjs. Horned Trunk-fish (Ostracion cornutus). 



living creature. The armadillo has only its back covered with this 

 bone armor, but, like the hedgehog and the manis, it can roll itself 

 into a ball with the unprotected parts inside. 4. In the turtles the 



