GENERAL ANATOMY OF THE LEECH. 161 



Two of these eyes are upon the first annulus. 



Two ui)on the second. 



Two upon the third. 



Two upon the fifth. 



Two upon the eighth. 



It is probable that each pair of eyes corresponds to a 

 body somite. The first annuhis must therefore be re- 

 garded as the first somite ; the second annulus as the 

 second somite ; the third and fourth annuli as the third 

 somite ; and the fifth, sixth, and seventh annuli as the 

 fourth somite. 



4. The two rows of black pigment spots along the 

 edges of the body. 



5. A median dorsal row of light-colored spots. Each 

 somite posterior to the fourth is made up of four or five 

 annuli, and the pigment spots are on the first annulus of 

 each somite. The body is thus seen to be made up of 

 twenty-five somites, without counting the posterior sucker, 

 which is shown, by its mode of development, to consist 

 of seven somites. 



6. On the dorsal surface in the groove which separates 

 the most posterior annulus from the sucker, notice the 

 anus. 



7. Make a drawing of the dorsal surface, to show these 

 points. 



f. On the ventral surface, notice : — 



1. The tnouth, bounded anteriorly and ventrally by the 

 proboscis, and ventrally by the ventral portion of the 

 fourth annulus. 



.2. A thickening of the median ventral portion of the 

 thirtieth annulus, in the centre of which the male repro- 

 ductive organ is placed. In specimens which have been 

 killed with chloroform, the penis usually projects a little 

 from the opening. 



