76 J. B. JOHNSTON. 



amount of blood in the ventral is due to the absence of the hearts 

 and the inability of the dorsal to drive the blood through the 

 capillary systems to the ventral. The absence of blood in the 

 posterior end is a further result of the small amount of blood 

 received by the ventral. If there were a segmental circulation 

 in Lnnibricns there would probably be no great accumulation of 



FIG. I. General scheme of circulation in body region, all the vessels of one seg- 

 ment being projected upon the plane of a transverse section. The vascular layer of 

 the intestine is shown by a broad black line. In the typhlosole the vascular plexus 

 thickens at one place to form the typhlosolar sinus which varies greatly in size in 

 different worms and in different parts of the same worm. From this sinus three dorso- 

 typhlosolar vessels in each segment carry blood to the dorsal vessel. These vessels 

 and the branching of the dorso-intestinal vessels shown in this figure have not before 

 been correctly described or figured for Lunibritiis. 



blood at the anterior end in these experiments, since the seg- 

 mental circulation would tend to relieve the systemic and the even 

 distribution of the blood would be maintained in accordance with 

 the law of least resistance. These regeneration experiments, 



