INTERNAL ANATOMY. 63 



bay, corresponding to each tongue-bar. (Cf. Fig. 29.) 

 This is what produces the sinuous, or notched, appearance 

 to the membrane in question, and led Johannes Miiller to 

 speak of it as the ligamentum denticulatum, (Cf. Fig. 28.) 

 The external or atrial opening of the tubule lies against 

 the tongue-bar at the head of this bay-like extension of the 

 atrial cavity (Fig. 31 on the right). 



The vascular supply of the tubules is effected in each 

 case by the co-operation of two blood-vessels ; namely, the 



Fig. 31. Plastic figure illustrating the blood-supply (glomeruli) of the excre- 

 tory tubules. On the right, the drawing is taken at a deeper level, to show the 

 atrial opening of the tubule over against a tongue-bar. (After BOVERI.) 



>J<. Cut edge of ligamentum denticulatum. c.v. Coelomic vessel of primary bar. 

 e.v. External vessel, i.v. Internal vessel, d.a. Left dorsal aorta. 



ca'lomic vessel of the primary bar (cf. Figs. 15 and 21) and 

 the external vessel of the secondary, or tongue-bar. As 

 soon as the coelomic vessel of a primary bar arrives at the 

 level of a tubule, it gives off a number of branches, which 

 not only anastomose among themselves, but become united 

 with a similar series of anastomosing vessels which origi- 

 nate from the external vessel of the next-following tongue- 



