No. 2.] ANATOMY OF BDELLODRILUS ILLUMINATUS. 531 



DESCRIPTIONS OF FIGURES. 



Unless specially stated otherwise, all drawings have been made upon camera 

 lucida tracings. With the exception of Figs. 28 and 40, which represent parts of 

 B. philadelphicus, all figures are drawn from preparations of B. illuminatus. 



EXPLANATION OF PLATE XXVIII. 



Fig. I. A diagram of the general anatomy of Bdellodrilus illuminatus showing 

 the principal organs, enlarged about eighty diameters. The entire vascular sys- 

 tem is colored ; the principal trunks and the dorsal and ventral enlargements of 

 the sinus being a darker, and the greater extent of the sinus a paler tint of the same 

 color. The post-cephalic somites are numbered i to 11; the four annuli antenor 

 to I constitute the head. 



Alimentary canal. P, pharynx ; cc. oesophagus ; S, two of the stomachic enlarge- 

 ment ; a, anus. In the seventh somite the intestine is hidden by the ovaries and 

 maturing ova. 



Vascular system. H, H, heart; va^-\ the seven pairs of vascular arches, of 

 which four are in the head, and one each in the ist, 7th, and 9th post-cephalic 

 somites ; S7t, sn, the supra-neural blood vessel; pa, the anterior, and//, the poste- 

 rior peri-enteric plexuses which terminate the sinus; s, sinus, the dorsal and ven- 

 tral enlargements are indicated by their deeper color. 



Nervous system, sg, principal, and sg\ the accessory supra-oesophageal gan- 

 glion; cc, the circum oesophageal connective; cg'-\ the three pairs of double 

 ventral cephalic ganglia; g'-\ the ganglia of the first eight post-cephalic somites; 

 gn, the posterior ganglionic mass. 



Reproductive organs, t' and t\ testes, represented as they appear in the im- 

 mature worm; vd^ and vd^ the anterior and posterior pairs of vasa deferentia; 

 ^, the male pore; bm, bm, the muscular walls of the copulatory bursa; bg, the 

 bursal glands; sv, the glandular, and sv\ the muscular sperm sac; Pe, penis; Ov, 

 ovary; 0^,0,, nearly mature ova; O \ smaller, but developing ova; 9 , female pore; 

 J/, sp\ and J/^ the undivided, the outer, and the inner divisions of the sperma- 

 theca, respectively. 



General nv, the common vesicle of the anterior nephridia; «A the termmal 

 portion of the nephridial tubule of the right side; Z^'"', lateral glands, dorsal and 

 ventral points of outlet shown for all, complete glands outlined in somites 2, 4. 

 and 8, the last a divided one. 



Fig. 2. A transverse section of a portion of the epidermis from the dorsum ot 

 the 5th somite. Kleinenberg's haematoxylin. X 500. Cellular zone to the nght, 

 non-cellular to the left of the figure, cc, cuticle; s/, striated lamina; ec, groups of 

 nucleated cells; sa, cleft or space in the protoplasm, d, d, dark column; cm, circu- 

 lar muscle fibres; «, nucleus. 



Fig. 3. Tangential section through region of Fig. 2, lettering the same, x 500. 



