ANATOMY OF THE EARTHWORM. 141 



thickening of the dorsal and lateral portions of about 

 seven segments from the twenty-ninth backwards. The 

 ventral portions of these segments are much less special- 

 ized than the upper portions. 



7. The delicate, chitinous, transparent cuticle which 

 loosely invests the external surface of the animal, and 

 M'hich may be slipped off from a specimen which has lain 

 for a few hours in water. 



8. The locomotor spines, or setae. In the earthworm, 

 these are so small that a lens is needed to detect them, 

 but if a worm be pulled backward gently between the 

 finofers, the resistance offered by the setae can be felt. 

 They are arranged in four longitudinal double rows, two 

 rows on each side, along the ventral surfaces of all the 

 segments except the fu'st, second, third, fourth, and last. 



The outer pair are on the line where the dark-colored 

 dorsal region shades off into the lighter-colored ventral, 

 and the inner pair are a little nearer the ventral median 

 line. 



9. The mouth is at the anterior end ot the body, and 

 leads into a large, eversible, buccal pouch. If a living 

 earthworm be held gently between the fingers, near the 

 anterior end of the body, the animal can be made to evert 

 this pouch. 



10. The anus, a small aperture at the posterior end of 

 the last segment. 



11. The segments and apertures of the body. 



a. The first segment is not a complete ring, and forms 

 a proboscis, or upper lip. 



b. The remaining segments are complete rings, and are 

 alike as far as the ninth. 



c. The ventral portions of the ninth, tenth, and eleventh 

 segments are thickened so as to form white glandular 



