CCELOM AND VASCULAR SYSTEM IN THE LEECH. 493 



pointed in the case of Hirudo ; if it were obliterated, the two 

 systems would still be in free continuity by means of capil- 

 laries. The botryoidal channels would seem to be rather of 

 the nature of a by-path, through which the haemolyniph does 

 not necessarily circulate. In this connection it should be 

 mentioned that in sections they are rarely seen to be as much 

 distended with the fluid as the neighbouring capillaries of 

 similar size. 



Whatever may be the process whereby the continuity be- 

 tween the coelom and vascular system has been established in 

 the Gnathobdellidae, there can be little doubt that it is a 

 secondary condition, and that the structure of such a form as 

 Acanthobdella, in which a closed blood-system lies in a normally 

 developed coelom, is really the more primitive. 



List of References. 



1. Bourne, A. G. — " Contributions to the Anatomy of the Hirudinea," 



' Quart. Journ. Micr. Sci.,' vol. xxiv, n. s., 1884. 



2. Burger, O. — " Neue Beitrage zur Entwickl. des Hirudineen," ' Zeit. f. 



wiss. Zool.,' vol. Iviii, 1894. 



3. Graf, A. — " Beitrage zur Kenntniss der Exkretionsorgane von N e p h 11 i s 



vulgaris," 'Jen. Zeit. f. Naturw.,' vol. xxviii, 1894. 



4. Gratiolet, p. — " Recherches sur I'organisatiou du Systeme vasculaire 



de la Sangsue medicinale," 'Annales des Sci. Nat. Zoologie,' vol. 

 xvii, 4th ser., 1862. 



5. Jaquet, M. — " Recherches sur le systeme vasculaire des Annelides," 



'Mitth. Zool. St. Neapel,' vol. vi, 1886. 



6. Johansson, L. — " Ueber den Blutamlauf bei Piscicola und Callobdella," 



' Festskrift Lilljeborg,' Upsala, 1896. 



7. Ko"WAXEVSKY, A. — " ^tude sur I'anatomie de I'Acanthobdella pele- 



dina," ' Bull. Acad. Imp. des Sci. de St. Petersbourg,' vol. v. No. 4, 

 1896. 



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



of the Medicinal Leech," ' Quart. Journ. Micr. Sci.,' vol. xx, n. s., 

 1880. 



9. Moquin-Tandon, A. — 'Monographie de la Famille des Hirudinees,' 



Paris, nouv. edit., 1846. 



