MORniOLOGY OF CYCLOSTOMATA. 347 



of the third pair shows a new character : the dorsal blind end 

 and the nephrostomal portion of the tubule are more or less expand- 

 ed, while these two portions are united by a slender middle trunk. 

 When compared with the tubule of the same pair on the opposite 

 side represented in figs. 81 and 82 [pLS), this character of the 

 tubule will be understood more clearly : the dorsal expansion is seen 

 in fig. 81, while the nephrostomal widening is observed in fig. 82. 

 The tubules of the following two pairs show the same feature. 

 On the right side of fig. 80, only the collecting duct between the 

 second and third tubules is found. The left tubule of the fourth 

 pair is shown on the left side of figs. 81 and 82 (pi. 4) ; fig. 83 

 shows a cross-section through the collecting duct (cd.) between the 

 third and fouith tubules and a slice of the anterior wall of the 

 right tubule {pt.4) of the fourth pair which is prolonged and bent 

 like the tubules of the last pair. The fifth pair of tubules is seen 

 on the left half of fig. 84 on one side (j^^.ô) and on the right 

 of fig. 85 on the other {pt.o). It is not developed as much as 

 the more anterior pairs, but shows considerable progress as com- 

 pared with the tubules in fig. 73 which represents the younger 

 stage of the same pair. 



These four pairs of the tubules (from the second to the fifth) 

 contain a spacious lumen and stand in wide communication 

 with the peritoneal cavity, which becomes, at the present stage, 

 conspicuous from this region forwards. 



In fio;. 86 which shows the fifth section behind the section 

 shown in fig. 85, the space on the left side which is occupied, 

 in the more anterior region, by the tubule or the collecting duct, 

 is replaced by the cross-section of a duct [scl.) with an oval out- 

 line and an ovoid lumen. This is the segmental duct under the 

 tenth myotome {mt.X). On the right side ol" the figure, however, 



