176 MICROSCOPY FOR BEGINNERS. 



serve locomotion. The egg is smooth, or hispid with 

 short hairs. 



8. Cn^ETONOTUS OCTONARIUS. 



This is a small, active form, readily recognizable by 

 the arrangement of the recurved dorsal spines. These 

 are unequally branched, and placed in two lateral lon- 

 gitudinal rows of three spines each, with one anterior 

 and one posterior central thorn. It seems to be the 

 least common of the species. 



9. CH^ETONOTUS SPINOSULUS. 



The back usually bears seven unequally furcate spines 

 in two transverse rows four spines in the anterior series, 

 three in the posterior. Occasionally the lateral thorns 

 in the posterior row are suppressed, and fn some indi- 

 viduals the front series contains but three. The lateral 

 body-margins are bordered by short, conical setae, which 

 are constant in all the specimens thus far observed. The 

 rest of the upper surface is without appendages of any 

 kind, except the four tactile vertical bristles present in 

 all species. The egg is hispid with short hairs. 



10. Cn^ETONOTUS LONGISPINOSUS. 



The spines vary from four to eight, the latter being 

 the usual complement. They are nearly one-half the 

 length of the body, and curve upward and backward in 

 a wide arch from the centre of the back. In front of 

 the anterior row the surface is setose with stiff, recurved 

 bristles, and the body- margins are fringed by coarse, 



