512 ANNELIDA. 



saddle-shaped, begins some way behind the segment of the male pores. Dorsal 

 pores present. Gizzard single, at end of oesophagus. Nephridia paired and 

 similar. No spenniducal glands or penial setae. Tubercula pubertatis nearly 

 always present. Cosmopolitan, but most characteristic of Palaearctic and 

 Nearetic regions. Allurus Eisen, male pores on 13 ; Tetragonus Eisen, male 

 pores on 12 ; Allolobophora Eisen, prestominm incompletely divides buccal lobe, 

 male pores on 15, no median seminal reservoirs ; A. lerrcstris Sav., spermathecae 

 in 9 and 10 resp. ; Lumbricus Eisen, prestomium completely divides buccal 

 segment, male pores on 15, two median seminal reservoirs occupying segments 

 10 and 11 into which open three pairs of sperm -sacs, spermathecae two 

 pairs, in 9 and 10 resp. ; L. rubellus Hoffm., clitell. 27-32, tubercula puber- 

 tatis 28-31, 1st dorsal pore 7/8. Male pores almost invisible ; L. hcrculeus Sav., 

 the common earthworm of this country, number of segments 180, clitelhun 

 32-37, tubercula pubertatis 33-36, 1st dorsal pore 7/8, male pores conspicuous. 



Class III. HIRUDINEA.* 



Elongated, vermiform Annelida icitli anterior and posterior suckers, 

 ///'fhout setae (except Acanfhdbdella) or parapodia, and ivitli median 

 genital openings. Coelom usually broken up into numerous inter- 

 communicating spaces. Hermaphrodite. 



The Hirudinea have, owing to certain superficial resemblances, 

 often been associated with the Trematoda, with which group they 

 have however nothing in common. They are in reality segmented, 

 coelomate animals with distinct affinities to the Oligochaetous 

 Chaetopoda. These affinities are specially obvious in the genus 

 Acanthobdella, in which there are setae in the anterior segments 

 embedded in pits in the body-wall, and a spacious body-cavity 

 divided by transverse septa into chambers. In the typical Leeches 

 the coelom is difficult to trace completely in the adult, but it is 

 undoubtedly present in the embryo in the usual Annelidan form of 

 a series of paired cavities in the mesoblastic somites ; and these 

 cavities give rise in the adult to the sinus system, and indirectly to 

 the tubes of the botryoidal tissue ; likewise, though in a modified and 

 A r eiled form, to the gonads and nephridia. A vascular system is 

 present, and by many anatomists is regarded as being continuous 

 with the sinus system ; but this continuity is doubtful, and in the 



* S. Apathy, " Siiss-wasser Hirudineen." Zool. Jahrb,, 3, 1888, p. 725. Id., 

 "Analyse der ausseren Korperform der Hirudineen," Naples MMheilungen, 8, 

 1888, p. 153. A.. Oka, " Beitrage z. Anat. d. Clepsine," Z. f. w. Z., 58, 1894, 

 p. 79. Fr. Leydig, "Circulations u. Respirationssystem v. Nephelis u. Clep- 

 sine," er. d. K. Zoot. Anst. zu Wiirzburg, 1849. Id., "Zur Anat. v. Piscicola 

 geometrica, etc.," Z.f.w.Z., 1. E. Ray Lankester, "On the connective and 

 vasifactive tissue of the medicinal leech/' Q.J.M. S., 20, 1880, p. 307. A. G. 

 Bourne, "Contributions to the Anatomy of the Hirudinea," Q. J. M. S., 24, 

 1884, p. 419. C. 0. Whitman, "The Leeches of Japan," Q. J. M. S., 26, 1886, 

 p. 317. A. Moquin-Tandou, Monographic des Hirudinees, Paris, 1846. 



