INTERNAL ANATOMY OF BDELI.A. 527 



line directed to the top of the Plate; it enters tlie peuial canal mucli below the head, but 

 looking down ])erpendicularly this is not appreciated. 

 Fig. 18. The penial canal, external labia, laminated gland, air-chamber, and parts of the azygous 

 accessory gland and glandidar antechambers seen from the side : x 120. 



19. One of the embedding-sacs after the testes and other organs have been removed from it, seen 



from within : X 70. The hollows in which the testes lay are shown ; the azygous accessory 

 gland, laminated gland, penial canal, and external labia are attached ; the labia are partly 

 seen from the exterior. 



20. The testes which have been removed from fig. 19, together with half the testicular bridge, one 



of the great mucous glands, the glandular antechambers, &c. : X 70. 



21. Central tube, hamuli, and detailed structure of penial canal : x 250. The outer wall of the 



penial canal is partly cut away so as to show the interior. 



22. One (the right) of the chitinous air-chambers which is sunk in the cmbedding-sac, from the 



exterior : x 200. The chamber has been dissected out of the sac. 



23. A portion of the interior of the laminated gland, showing the principal laminte and the oblique 



lesser lamclhe : X GoO. 



24. Genital organs of young female in situ, the oviduct being only slightly uncurled: x 120. The 



reeeptaculum seminis is hidden. 



25. Genital organs of young virgin female (reared) of Bdella vulgaris, slightly spread out; but the 



curl of the oviduct is natural. 



26. Perpendicular section through one of the eyes : x 550. 



27. Horizontal section through the terminal part of the optic nerve and the retinal discs : x 200. 



The section cuts the lower eye through the rods (retiuulee), the cells of the disc only 

 showing near the periphery ; the upper eye is cut wholly in the retinal disc. 



28. Transverse section of the oesophagus between pharynx and braiu, to show the irregular shaped 



lumen : x 650. A typical section was selected, but probably no two sections were ever 

 really similar ; they vary widely. 



29. Maxillary lip from below : x 80. 



30. The mandibles in. situ, seen from above : x 80. 



31. The left mandible seen from the inner (flat) side : x 80. 



32. Terminal portion of maxillary lip from below, showing the membranous flaps inside (above) the 



lip : X 450. The lip has been flattened out to show the flaps ; in reality when the lingua is 

 not protruded the sides of the lip curl upward and the two flaps lie against each other, 

 closing the entrance anteriorly. 



33. A small portion of the external cuticle showing the wavy irregular ridges composed of long- 



shaped raised dots, joined by the lower parts of the ridge : x 550. 



Plate 43. 



Fig. 34. Median sagittal section of male : x 50. The section is a thick one, so as to show some organs 

 which are not in the actual median plane where they are not hidden by other organs which 

 arc in that plane. Thus one mucous gland is shown with a portion of the azygous accessory 

 gland and the genital nerve passing over it. The caeca of the ventriculus have practically 

 closed over the excretory organ from the pressure of food-coutents and other causes. 

 Numerous small traclie:e (not lettered) are seen between the brain and the ventriculus and 

 mucous gland. The resophagus is seen passing through the brain, and the reeeptaculum 

 cibi (sucking-stomach) sjirings from its dorsal side. The cells of the ventriculus are crowded 

 with food-droplets, the excretory organ with the usual white matter. 



