ANATOMY AND PHYSIOLOGY 



77 



FIG. 92. 



extend through a pore canal into the interior of the hair (Fig. 

 91) ; sometimes, to be sure, as in glandular or sensory hairs, 

 the hair cell is multinucleate, rep- 

 resenting, therefore, as many cells 

 as there are nuclei. The wall of 

 a hair is continuous with the gen- 

 eral cuticula and at moulting each 

 hair is stripped off with the rest 

 of the cuticula, leaving in its place 

 a new hair, which has been form- 

 ing inside the old one. 



Scales. -- Besides occurring 

 throughout the order Lepidoptera 

 and in numerous Trichoptera, 

 scales are found in many Thys- 

 anura and Collembola, several 

 families of Coleoptera (including 

 Dermestidse and Curculionidse), a 

 few Diptera and a few Psocidse. 



Though diverse in form (Fig. 

 92), scales are essentially flattened 

 sacs having at one end a short 

 pedicel for attachment to the in- 

 tegument. The scales usually bear markings, which are 

 more or less characteristic of the species; these markings, 

 always minute, are in some species so exquisitely fine as 

 to test the highest powers of the microscope; the scales 



of certain Collembola (Lepi- 

 docyrtus, etc.) have long been 

 used, under the name of 

 " Podura " scales, to test the 

 resolving power of objec- 

 tives, for which purpose they 

 are excelled only by some of the diatoms. Butterfly scales 

 are marked with parallel longitudinal ridges (Fig. 92, C), 

 which are confined almost entirely to the upper, or ex- 



Various forms of scales. 

 A, E, thysanuran, Machilis; B, 

 beetle, Anthrenus; C, butterfly, 

 Pieris; D, moth, Limacodes. 



Cross section of scale of Anosia. 

 After MAYER. 



