422 ALFRED GIBBS BOURNE. 



9, Leuckakt, Rudolf. — 'Die Menschlichen Parasiten,' Leipzig und 

 Heidelberg, 1863. 



10. Leydig, Dk. Franz. — " Vom Bau des thierischen Korpers," ' Hand- 



buch der vergleichenden Anatomie,' Erster Band, Tubingen, 1 864. 



11. Bidder. — ' Untersucliungen ueber das Blutgefassystem einiger Hiru- 



dineen,' Dorpat, 1868. 



12. Vaillant, Leon. — " Contribution a I'l^tude Anatomique du Genre 



Pontobdelle," ' Annales des Sciences Naturelles '— " Zoologie," 5 

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13. Gegenbaur, Carl. — ' Elements of Comparative Anatomy ' (Lankester's 

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l^. Whitman, Charles Oxis. — " The Embryology of Clepsine," 'Quar- 

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15. Hoffmann, Dr. C. K. — ' Untersuchungen ueber den Bau und die Ent- 



wickelungsgeschichte der Hirudineen,' Haarlem, 1880. 



16. Lankester, E. Ray. — " On Intra-epithelial Capillaries in the Integu- 



ment of the Medicinal Leech," ' Quarterly Journal of Microscopical 

 Science,' vol. xx, New Series, 1880. 



17. Lankester, E. Ray. — " On the Connective and Vasifactive Tissues of 



the Medicinal Leech," ' Quarterly Journal of Microscopical Science,' 

 vol. XX, New Series, 1880. 



18. Bourne, A. G. — " On the Structure of the Nephridiaof the Medicinal 

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19. Lang, Dr. Arnold. — Der Bau von Gunda Segmentata und die Ver- 

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ii. External Characters. 



The question which I attempt to answer here may be thus 

 stated : — How far in the series of Hirudinean genera do ex- 

 ternal characters express the metamerically segmented nature 

 of their organisation ? 



The essential difference between the annulations of a leech 

 and those of a bristle-bearing worm seems to have first struck 

 the mind of De Quatrefages/ while Gratiolet^ for Hirudo 



I ' Ann. Sci. Nat. Zool.,' 1852, p. 285. 



3 ' Ann. Sci. Nat. Zool.,' 1862, pp. 178, et seq. 



