PLATE I. 



Nervous system blue. Alimentary canal green. Heart and blood-sinuses red. 



Cloaca-ducts yellow. Appendages of the cloaca-ducts brown. 



Integument, cloaca-wall, copulation-spicula, blood-gland, pericardium and muscles black. 



Fig. I — 22. Proneomenia Weberi. 



I'roneomenia Weberi, 4 ■ , drawn from spirit-specimens. 



Spicula 125 X. A of the body-wall, £ cloaca-spicula, C spicula from the hinder body-region, 



D along the ventral groove. 

 Schematic sections along the lines AB — A^O of fig. 11. 28 y. See te.xt. 

 Reconstruction out of transverse sections of genital glands, pericardium, cloaca-ducts, part 

 of the cloaca and digestive canal. Dorsal view, c copulation-spiculum. 28 • . 

 Fig. 12. Epithelium of the wall of the cloaca-pouch l> (cf. fig. 5), a cavity in which a cloaca- 



spiculum. 215 • . 

 Fig. 13. Reconstruction of the anterior part out of longitudinal sections. / wall of the pharyn.x, 



a part of the mouth-cavity, enclosed by the "Mundlcisten", in which the cirrhi are 

 found, d muscles of the pharyngeal fold. 28 X. 

 Figs. 14 — 16. Schematic transverse sections of the anterior part, cf. the lines AB — /: F of fig. 13. 



5 septum, cc cartilaginous cells of the radula. 28 ■ . 

 Fig. 17 yi. A longitudinal section through the radula. a radula-sac, /; epithelial pouch. See text, ^y X. 



B. A transverse section; the greater part of the teeth are broken. ^/^ x. 



C. Row of teeth of the radula, isolated with Eau de Javelle. 88 X. 

 Fig. 18 A. Transverse section through a cloaca-duct. 



B. Transverse section through the vesiculae seminales. 190 > . 

 Fig. 19. Transverse section through a copulation-spiculum with its muscular bundles. 125 X- 



Fig. 20. Longitudinal section through the base of a copulation-spiculum (see te.xt). 150 X. 



Fig. 21 A. Idem. /> protractors, ;• retractors. 28 X. 



B. Point and middle piece of a copulation-spiculum, isolated with Eau de Javelle. 125 X- 

 Fig. 22. 5 Transverse sections through the pericardium with the heart. 



A a the two distal pericardial invaginations, forming together : 



B a the atrium. 



Cv the ventricle. 



D av the right atrio-ventricular opening, with little sphincter. 56 X. 



Figs. 23 — 40. Proneomenia longa. 



Fig. 23. Proneomenia longa, 4 ■ , drawn from the spirit-specimen. 



Fig. 24. Transverse section through the mouth-opening, along line A B o{ fig. 27. 24 X. 



Fig. 25. Papillae of the integument. 315 ■. 



Fig. 26 A. Transverse section through the radula, 



B. A hooked tooth. 190 X. 

 Fig. 27. See plate II. Reconstruction of the anterior part, out of transverse sections, a part of 



the mouth-cavity filled with cirrhi ; b epithelial pouch of the radula. 24 X. 

 Fig. 28. Transverse section through the radula in pouch b (cf. fig. 17 A). 190 \. 



Fig. 29. Transverse section somewhat more distally ; the teeth have disappeared ; cuticular matter 



is formed. 190 ',\. 

 Figs. 30 — 35. Schematic transverse sections through the posterior extremity. 28 ■. ag preanal gland, 



cs copulation-spiculum. 

 Fig. 36. Transverse section through the heart, p pericardium, a atrium, bilobed, k invagination of 



the dorsal pericardial wall, forming the ventricle more proximally, rti' left atrio-ventricular 

 opening with sphincter. 88 • . 

 Transverse section through the radula-sac. 215 X. 

 Epithelium of the dorsal cloaca-wall. 388 X. 

 l^pithelium of the lateral cloaca-wall. 215 >X 



Transverse section through the posterior end of the second specimen, cf. fig. 33. cs small 

 copulation-spicula. 25 X. 



