MICROSCOPE IN-DOORS. 83 



pillar are furnished with a series of barbs, which, 

 when they once penetrate the skin, are not easily 

 removed, as seen in figure 189, plate 7. 



Spiders are frequently covered with hairs, some 

 of which are branched, as at a in figure 190; 

 others present a spiral appearance, seen at b ; 

 whilst, again, others offer a series of small bristle- 

 like hairs running down each side of the primitive 

 hair, which will be seen at c. 



Many of the Crustacea have hairs upon their 

 shells. Those upon the flabellum of the common 

 crab have minute bristles on one side of the parent 

 stalk, so as to form a little comb, with which to 

 brush off the impurities from its branchiae. This 

 structure is seen at figure 191 in plate 7. A live 

 crab from the aquarium may be watched for the 

 purpose of observing these cleanly movements. 



The study of the uses of the epidermal ap- 

 pendages is one full of interest, as in no one 

 set of structures do we find a greater variety of 

 adaptations of a common plan to the wants of the 

 creatures in which they are found. The feathers 

 of birds belong to the same type of structure as 

 the hairs of animals. If the pinnae of a common 

 goose-quill, used for a pen, are examined, the 

 pinnules will be found to be covered with minute 

 hooks, drawn in figures 192 and 193, plate 7. These 

 hooks on the upper surface are so arranged that they 

 catch the nearly plain and slightly toothed pinnules 

 on the lower side. 



The down from the feathers of the swan, with 

 which pillows and beds are stuffed, is also a beau- 

 tiful object, and its microscopic structure will at 

 once reveal the cause of its lightness, softness, and 

 warmth. This is seen at figure 194, in the 7th 

 plate. 



Amongst the creatures which domesticate with 

 a 2 



