CIRCULATION OF THE OELOMIC FLUID IN A 



NEMATODE. 



FREDERIC H. KRECKER. 



The nematodes are not known to have a special circulatory 

 system and it has been rather generally considered that they do 

 not possess a circulating medium. 



In some nematodes of the genus Camallanus taken from the 

 rectum of a sun fish (Apomotis cyanellus] I noticed a flowing 

 movement of the ccelomic fluid. It was blood red and could 

 therefore be easily distinguished. Waves of the fluid passed 

 from the anterior to the posterior end and then in the reverse 

 direction. 



The reversal of the circulation calls to mind the condition 

 in ascidians. In them it will be remembered, there is a clearly 

 defined circulatory system and the reversal of blood flow is due 

 to the heart forcing the blood first in one direction for twenty 

 or thirty beats and then, after a pause, sending it in the opposite 

 direction. The only similarity in these two instances lies in the 

 fact that in both of them the circulating medium is impelled first 

 in one direction and then in the other. 



Before describing fully what occurs in these nematodes it 

 might be best to point out briefly such of their structural features 

 as have a bearing on the phenomena. The specimens at hand 

 are all females from 20 to 25 mm. long. As commonly happens 

 among nematodes the uterus extends practically the entire length 

 of the ccelom. It is so distended with embryos that in optical 

 section it appears to be in contact with the body wall. As a 

 matter of fact there is just enough space between the two for a 

 thin layer of coelomic fluid. 



The circulation of the fluid is brought about by peristaltic 

 contraction of the uterus. The ability of these constrictions to 

 force the fluid along is due to there being more of it than can be 

 accommodated in the narrow peri-uterine space. A sharp con- 

 striction of the uterus forms a comparatively deep depression 



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