STUDIES ON EARTHWORMS. 107 



Diachseta Thoniasii. 

 Fig, 22. — Dorsal view of the first thirty-nine somites, showing the scattered 

 and alternating arrangement of the setae. ( X 3.) cl. Clitellum, occupying 

 somites xx to xxxiii. r. Kidge in the somites anteriorly to somite x. 



Fig. 23. — View, from below, of a portion of the body wall which has been 

 cut along the dorsal mid-line and pinned out, so as to show the alternating and 

 asymmetrical arrangement of the setae, which are numbered 1 to 7. (x 10.) 

 a. The nephridiopores. c. The spermathecal pores, d. Setae, 1, 2, 3, corre- 

 sponding to the ventral couple of Lumbricus. e. The setae, 4, 5, 6, 7, 

 corresponding to the lateral couple. 



Fig. 24. — Ventral view of three somites of the clitellum, which has been 

 cut along the dorsal mid-line and spread out. a. The nephridiopores. b. 

 The pores of the sperm-duct. d. The ventral setae, e. The lateral setae. 



Fig. 25. — A seta; nat. size 0"25 mm. 



Fig. 26. — General view of the worm, when opened from the dorsal surface 

 the spermathecae have been straightened out in order to show their position 

 the gizzard, &c., are hidden by the strong septa. ( X 3.) a. The supra 

 pharyngeal ganglia, b. The pharynx, c. The modified first nephridium 

 d, d. The spermathecae. e, e. The strong septa behind the somites vi to x 

 f. The ciliated rosette, g. The seminal reservoir, h. The dorsal blood 

 trunk. j,j, Nephridia. h. The sacculated intestine. I. A lateral heart. 



Fig. 27. — A nephridium. a. The coiled tubule, b. Vesicular portion or 

 ducr,, being a continuation of the tubule, c. The portion of the duct leading 

 to the nephridiopore. f. The funnel. 



Fig. 28. — One of the first pair of nephridia (" glandes a mucosite " of 

 Perrier). a. The glandular-looking mass of tubules, b. The vesicular 

 portion or duct. c. The exterufil aperture which is placed on the anterior 

 edge of somite ll. 



Fig. 29. — A spermatheca. 



Fig. 30. — A portion of the nerve-cord, showing four closely placed ganglia, 

 with the lateral nerves. 



Trigaster Lankesteri. 



Fig. 31. — Ventral view of the first fifty somites ; the body wall has been 

 cut along the dorsal mid-line and pinned out. (X 2.) a. The prostomium. 

 b. The mouth, c. The lateral setae, d. The ventral setae, e, e. The sper- 

 mathecal pores. /,/'• The papillae forming the sides of the median fossa, g. 

 The median genital fossa, h. The clitellum occupying somites xiv to xl. 



Fig. 32. — Two somites further enlarged, to show the three grooves whicn 

 surround the somites, a. A more or less prominent ridge in the anterior 

 somites, c. The lateral, and d. the ventral setae. 



Fig. 33. — The alimentary tract, together with the septa, removed from the 

 body. (X 4.) a. The buccal region, b. The pharynx, c, d, e. The three 



