HAIR. 



[ 377 ] 



HAIR. 



pigment is met with sometimes in the me- 

 dulla, at others in the cortex. The arrange- 

 ment of the air-cells is often very beautiful, 

 and has rendered these hairs favourite 

 microscopic objects. Portions of a mouse- 

 hair in various parts of its length are re- 

 presented in fig. 27, a forming the free end. 

 Fig. 28 displays two portions of the same 

 hair as histolyzedby treatment with solution 

 of potash. The cortical parts have not been 

 resolved into their component cells, whilst 

 those of the medulla have assumed their 

 rounded and natural form, and exhibit mi- 

 nute granules of pigment, with larger glo- 

 bules of fat. The arrangement of the me- 

 dullary cells in two rows is seen in fig. 28 b. 

 The pigment within the cells in situ is seen 

 in fig. 31 6, from the rabbit. The wool 

 presents its characters in a marked degree, 

 the projection of the outer layer of cortical 

 cells and the distinctness of the medullary 

 air-cells being very evident. 



Marsupialia (figs. 36 & 37). In this cu- 

 rious Order the hair greatly resembles that 

 of the Rodents. That of the kangaroo pre- 

 sents very beautifully imbricated cortical 

 cells (fig. 36). 



Monotremata. The structure of the hair 

 of the Ornithorhynchus is as peculiar as 

 that of the animal in general. It presents 

 that of hair and wool combined (fig. 38). 

 The basal portion resembles wool, and is 

 very long and narrow ; the structure of two 

 pieces in different parts of its length is seen 

 in fig. 38 c and d. At the end of this por- 

 tion is attached the proper hair containing 

 the pigment within the cortical substance 

 (b) ; tig. 38* represents the surface-view of 

 the hair, showing the imbricated scales. 



In Birds the hair is replaced by FEA- 

 THERS. 



The hair of the Invertebrata does not 

 present the same structure as that of the 

 higher animals ; some physiologists have 

 therefore limited the term hair to the fili- 

 form epidermic formations of the Mam- 

 malia, whilst others admit the occurrence 

 of hair in all classes of the animal kingdom. 

 At all events, the hairs of the Invertebrata 

 are not usually composed wholly of epider- 

 mis. They consist of an outer cortical or 

 epidermic layer, frequently coloured, and 

 upon which their firmness depends ; lining 

 this is sometimes a prolongation of the 

 cutis, at others a colourless substance which, 

 when the hair is dried, presents an irregular 

 cell-like appearance and contains air, so as 

 o resemble the air-cells of the hair of the 



Mammalia. In other instances the hair is 

 completely solid, but exhibits no trace 

 whatever of cell-structure. It remains to 

 be shown whether the latter may represent 

 the epidermis hardened in an amorphous 

 state, and whether those lined with cutis 

 may be regarded as epidermic formations 

 upon an exserted papilla of the skin -, whilst 

 those presenting the air-cells when dried 

 correspond to an outer hardened epidermic 

 layer, and an inner retaining its distinctly 

 cellular state. In those lined with cutis, 

 the circulation can sometimes be observed. 



We have space to notice only a few in- 

 stances of variety of form, many of which 

 occur, and have long rendered these hairs 

 interesting and elegant microscopic objects. 

 Thus, in some of the Arachnida they are 

 feathery, giving oft' slender lateral branches, 

 as in Lycosa (PI. 29. fig. 40), Epeira (PI. 6. 

 fig. 8 6), Acarus (PI. 6. fig. 1 b), &c. j in 

 others these branches are directed forwards 

 near the middle of the shaft, but recurved 

 at the end, as in Mygale (the bird-catching 

 spider) (PI. 29. fig. 41); or, while the 

 branches on the shaft resemble the above, 

 the end of the hair is thickened, cylindrical 

 and longitudinally striated, with minute 

 setae arising from the striae, as in fig. 42 ; 

 again, some of them are simple, but fur- 

 nished with spiral striae (Epeira, PL 6. 

 fig. 8 a) ; in Trombidium they are sometimes 

 very elegantly feathery. 



In Insects, Arachnida, &c., they often 

 appear to rise from a bulb at the base ; but 

 the bulb is not solid, and bears no resem- 

 blance in structure to the bulb in the 

 Mammalia; it consists of a thickening or 

 fold of the epidermis of the skin, not of the 

 hair, from which it is separated by a white 

 ring, indicating thinness of this coat, and 

 often corresponding to a joint; the hair 

 arises from the base of a depression situated 

 within the annular bulb. The hair of some 

 of the larvae of the Dermestidae is very 

 beautiful, and is used as a TEST-OBJECT. 

 Two forms are met with : in one (PI. 1. 

 fig. 1 c) the shaft is simply covered with 

 densely aggregated, minute, spinous secon- 

 dary hairs; in the other (PI. 1. fig. 1 a, 6), 

 the spines or scales upon the shaft are nar- 

 row, acute, and placed in pretty regular 

 whorls ; in the uppermost whorl they are 

 broader, the spines remaining as midribs, 

 whilst the margins are more developed, the 

 whole resembling a flower with four or five 

 petals; but at the end of the hair, the 

 scales are longer, narrower, and recurved, 



