41 8 WHITMAN-. 



EXPLANATION OF PLATE XV. 



Letters. 



I-XXVI = somites. 



1-66 = rings. 



(4-72) = corresponding rings of C. chelydrcE. 



b. 5-6 = buccal rings. 



pb. 7-8 = post-buccal rings. 



/. = lateral row of sense-organs. 



ni. — median row of sense-organs. 



nig. = marginal row of sense-organs. 



npA, = nephridiopores. 



0/. — outer lateral row of sense-organs. 



Fig. I. — Diagram of the anterior portion of Clepsine plana. The first ring 

 bearing the single pair of eyes is double, and corresponds to the fourth and fifth 

 rings in C. chelydra, which appears to be the more typical form. The second ring 

 is also double, and equivalent to the sixth and seventh of C. chelydrce. The numbers 

 inclosed in parentheses in this and the two following figures refer to the same species. 

 Dotted areas show distribution of the yellow pigment. X 5. 



Fig. 2. — Ventral surface of four rings from the middle of the body, showing the 

 longitudinal pigment-lines and the relative position of the sense-organs, as well as the 

 nephridial pores. X 5- 



Fig. 3. — Diagram of the posterior portion of the leech, prepared with especial 

 reference to the topographical relations of the sense-organs and the annular compo- 

 sition of the last four somites of the body. % X 5- 



