ON THE BLOOD VESSELS, THEIR VALVES AND 



THE COURSE OF THE BLOOD 



IN LUMBRICUS. 1 



J. B. JOHNSTON. 



In a previous paper - an account has been given of the experi- 

 mental study of the course of the blood flow in Lumbricus 

 The most important result there set forth was that the circula- 

 tion is not segmental but strictly systemic. The course of the 

 flow is as follows : forward in the dorsal vessel for its whole 

 length ; downward in the hearts ; both forward and backward 

 from the hearts in the ventral vessel ; outward from the ventral 

 to the body wall, nephridia and intestinal wall ; toward the lat- 

 eral neurals from the body wall ; backward in the subneural ; 

 upward to the dorsal vessel in the parietals from the subneural, 

 the nephridia, and the body wall, and in the dorso-intestinals 

 from the intestine. Thus, there is no circuit of blood in each 

 segment to which a sytemic circuit for part of the blood has 

 been superadded, as all previous authors have maintained, but 

 all of the blood flows in a single systerryc circuit. In the head 

 region the blood is carried forward beyond the hearts by both 

 dorsal and ventral vessels and is returned to the dorsal behind 

 the hearts in larger part by the lateral cesophageals, and in smaller 

 part by the subneural and the parietals of XII. and succeeding 

 somites. The lateral cesophageal system is considered to repre- 

 sent the parietals in the somites anterior to XII. 



This view of the circulation raised two important questions 

 which further work has answered : (i) What happens when the 

 hearts are removed from the circulation by decapitating the 

 worm ? Do the conditions which obtain in the regenerating 



1 Studies from the Zoological Laboratory of West Virginia University, No. 8, 

 February 28, 1903. A part of the work reported here was done by my former stu- 

 dent, Miss S. W. Johnson. For the conclusions reached the present writer alone is 

 responsible. 



' 2 " The Course of the Blood Flow in Lumbricus," by J. B. Johnston and Sarah 

 W. Johnson, Amer. Naturalist, April, 1902. 



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