ON MONOPYLEPHORUS LIMOSUS. 



33 



becomes less obtuse and finally a right angle (fig. 28). The two 

 ends of the transversal bridge are continued into a lateral horn, in 

 which we may again distinguish a dorsal and a posterior portion. 

 The dorsal portion of the lateral horn is the most dorsal part of the 

 spermiducal chamber and lies near the lateral line, its lower part touch- 

 ing the dorsal wall of the transversal bridge. The posterior portion of 



the lateral horn is a large, 

 posteriorly directed pro- 

 cess given off from the 

 hind end of the dorsal 

 horn and the transversal 

 bridge and reaching to 

 the posterior septum. 

 The widest part of the 

 lateral horn is about 

 equal to or slightly larger 

 than that of the atrium. 

 As soon as the 

 atrial duct portion passes 

 over into the dorsal portion of the lateral horn, the lumen widens 

 suddenly and in the posterior portion it reaches to the hind end, 

 whence it is continued forwards, on the ventral side of its fore- 

 going portion, to the lateral termination of the transversal bridge. 

 As a general rule, the inner surface shows irregular folds in the 

 lateral horn, but is smooth in the transversal bridge, the cavity of 

 which is more or less flattened dorso-ventrally and passes into the 

 median chamber, which opens directly to the exterior on the ventral 

 median line of the body. 



The wall of the spermiducal chamber consists of five layers 

 which are direct continuations of those of the body wall. The 

 innermost cuticular layer is very thin and shows no markings. 



Fig. 28. 

 Cross section through segment XI of a fully mature 

 specimen, showing the transversal bridge and the median 

 male pore. Clitellar gland cells are very well developed. 

 xl50. Cœlomic corpuscles omitted, tb — transversal 

 bridge, n.c— ventral nerve cord, c — cuticle, ch — clitellar 

 hypodermis, oh — ordinary hypodermis, sp — spermatozoa. 



