PREFACE. 13 



three dijfferent kinds of appendages. These different 

 regions are technically called head, thorax, and 

 abdomen. In walking, owing to the disuse of cer- 

 tain of the abdominal or fleshy false legs, the cotton- 

 worm doubles the body between the thorax (which 

 bears the true jointed legs) and the 7th abdominal 

 segment. This position of the body gives it the 

 name of a half-looper. As it grows, the yellowish- 

 green cotton-worm casts its skin from time to time, 

 feeding all the while and growing rapidly. The 

 segments of the body are seen to be ornamented 

 with black dots, which, under the microscope, ap- 

 pear as warts, some of which give rise to hair. In 

 some of the worms there is a distinct dorsal line 

 visible, wanting in others. This stripe down the 

 back gives the worms a peculiar appearance : it 

 seems to be a variation, the colour due to the mass- 

 ing of pigment-cells in the skin, and not a reflec- 

 tion of the digestive system of the animal, which 

 begins at the mouth and ends at the last segment, 

 through the opening of which the leaf-food of the 

 animal is expelled in little pellets. This variation 

 of the markings of the cotton-worm is interesting, 

 because it shows the worm to be undergoing some 

 slow process of modification ; and it may be that its 

 present mode of life in the Southern States is pro- 

 ducing some change in itself. 



In Central Alabama, I have watched the growth 

 of the worms on the cotton-plant. The worm ap- 

 pears there in certain seasons as early as the latter 

 part of June. After feeding for a period of 

 about fourteen bays, the cotton-worms begin prepa- 



