THE HORNY SKELETON. 229 



all three layers of the integument, but merely of the epidermis : they 

 are thickenings, and also often folds of this cuticle, between which a 

 coloured mucous has inserted itself. The corium is wholly wanting in 

 these excrescences. They are divided according to their form, and the 

 mode of their connection with the integument, into three different 

 groups. 



J. SPINES differ from the following kinds by their wanting a true 

 root. They are therefore nothing else than pointed, spinous, conical or 

 hair-shaped processes, which rise from the surface, and correspond 

 with it in colour and clothing. As a clear proof that they are mere 

 processes of the epidermis, or, when they appear more bossed (as in the 

 great horns of the Lamellicornia) , that they are true elevations of the 

 entire integument, is evinced by the circumstance that they produce a 

 hole in the horny substance exactly of their own dimensions when 

 broken off. These spines are not always simple, they are frequently 

 ramose, furcated, &c., as is observed in many of the caterpillars of 

 the butterflies. 



2. HAIRS are distinguished from spines in the first place by their 

 greater fineness and lesser compass, in combination with their pro- 

 portionately greater length, and again by the root by which they are 

 attached to the true skin. The hairs themselves are fine horny 

 cylinders, which frequently split and divide themselves like feathers, 

 and send off branches, thus acquiring a resemblance to the feathers of 

 birds. In general, they are largest in compass at their centre, and 

 become narrower towards both ends : the lower one is somewhat puffed 

 out, and has a small knob which sticks in the corium like a bulb in the 

 earth, and this is surrounded by a thin shell, exactly as is the case in 

 the large beard bristles of the mammalia. 



3. The SCALES are properly flattened hairs : this is shown not only 

 by their gradual transition from linear to lanceolate and spatulate 

 forms, but also their exactly similar connection with the integument. 

 Each scale, namely, has a small pedicle, at the end of which the 

 knobby root is placed, and this with its sheath is inserted in the skin. 

 The scale itself is either round, pointed, forked, toothed like a saw 

 in front, and provided with longitudinal furrows upon its superficies. 

 Even this delicate and sometimes extremely fine membranous ex- 

 crescence consists of two layers of the epidermis, between which the 

 pigment has inserted itself. In the iridescent butterflies (Apatura 

 Iris, A. Ilia, Papilio Adonis, Menelaus, fyc.), the scales of the wings 



