630 THE ANIMAL KINGDOM. 



growth of connective tissue, which splits it up into sinuses and channels, a 

 process termed diacoelosis. This tissue may in its turn undergo meta- 

 coelosis, i. e. become secondarily hollowed out, a process most marked in 

 Nephelis and Trocheta (Bourne). There are four main sinuses in the 

 Rhynchobdellidae, a dorsal, a ventral which always lodges the nerve-cord, 

 and two lateral. The dorsal and ventral sinuses are alone present in 

 Gnathobdellidae, and the former is sometimes absent (Nephelis, Trocheta). 

 Coelomic epithelium is found lining the sinuses in the former group, but not 

 in the latter. There are other remnants of the coelome round the genera- 

 tive organs, &c., but different Leeches vary much in these points. The 

 blood is colourless in Rhynchobdellidae, but in the Gnathobdellidae the 

 plasma is red with haemoglobin. There are colourless amoeboid corpuscles, 

 and in some Gnathobdellidae at least nuclei set free from the excavated 

 connective tissue cells. 



The excretory system consists in Pontobdella of a network of tubules 

 lying within the muscular layers, continuous from side to side of the body, 

 and provided with ten pairs of segmentally arranged nephridial funnels and 

 as many external openings. There appears to be a similar network in 

 Branchellion and Piscicola. The latter has also ten pairs of external aper- 

 tures. In Clepsine and other Hirudinea, so far as is known, the nephridia 

 are paired organs, independent of one another, and complicated in structure. 

 In Hirudo and its immediate allies, the nephridial duct terminates in a con- 

 tractile vesicle which opens externally. The ciliated nephridial funnel is 

 rudimentary in Hirudo, Haemopis, Haemadipsa, or occasionally occluded 

 as in Pontobdella. It lies in a blood, i. e. coelomic sinus ; the ventral sinus 

 in Clepsine ; a dorso-ventral sinus in Pontobdella ; a small isolated remnant 

 of a sinus in Hirudo, &c. ; or in a metacoelome excavated in botryoidal 

 tissue, as in Nephelis and Trocheta. The ductules in the secreting part of 

 the gland ramify in the gland-cells. The external nephridial aperture is 

 ventral or marginal in Haemadipsa japonica, and on the first annulus of a 

 somite in Pontobdella, on the last in Hirudo 1 . 



The Hirudinea are hermaphrodite. The apertures of the male and 

 female organs lie near one another in the median ventral line, the male in 

 front of the female. The testes vary in number from five to twelve pairs 

 segmentally arranged, or a much larger number not arranged segmentally 

 as in Nephelis, and connected, each testis by a separate duct, to a common 



1 Whilst the Leech, and more especially the Land Leech of Japan, is engaged in sucking, a clear 

 fluid covers it and may fall in drops. It is derived chiefly if not entirely from the nephridial vesicles, 

 and may be seen to exude from their external pores. The organs in question may therefore serve as 

 a storehouse of liquid to moisten the skin. They are peculiarly large in the Land Leech, and the 

 three pairs opening within the limits of the clitellum have a thick cubical epithelium disposed in 

 folds. It is possible that they furnish some of the liquid contents of the cocoon. The epithelium of 

 the vesicles in other parts of the body is a pavement epithelium. See Whitman, op. cit. p. 327, pp. 

 The Japanese Land Leech leaves a slimy track like a snail's behind it as it crawls. 



