SANGUIFEROUS SYSTEM. 439 



with the genital apparatus. The plan of the circulating 

 system is similar in the polystomum and octobothrium, and 

 from the limpid and homogeneous character of the blood, and 

 the inert condition of the vessels in which it is contained, 

 neither the motion nor the presence of that fluid is percep- 

 tible in the transparent canals of the caryophyllaus, nor is 

 any motion perceptible in the vessels which convey the 

 blood in the aspidogaster. But in the lernaa, globules of 

 different sizes abound in the limpid blood, and distinct pul- 

 sations are observed in the great central artery of the trunk, 

 as in the higher tribes of articulated animals. In some of 

 the highest entomoid forms, as the achtheres, a distinct 

 elongated pulsating cavity is seen extending along the middle 

 of the anterior part of the cephalothorax, which sends two 

 vessels laterally to the prehensile fixed arms, and two similar 

 canals posteriorly to the viscera, thus approaching to the 

 form of the sanguiferous system of the Crustacea. By the 

 pulsations of the dorsal vessel the blood is sent rapidly 

 through the canals of the arms and of the abdomen ; but in 

 the following in stance it appears to re turn by the same passages, 

 as if they performed the functions both of arteries and veins. 

 From the transparency and the colourless texture of the 

 body in the rotiferous animalcules, vibratile cilia are percep- 

 tible on the exterior peritoneal surface, and the interior mu- 

 cous lining of their alimentary canal, and producing rapid 

 currents of water through the lateral brancheal tubes and 

 tufts disposed along with the extended testes, in the capa- 

 cious cavity of the abdomen. These more obvious r,espira- 

 tory currents appear to have been mistaken for a circulation 

 of blood, which has not been distinctly perceived to move in 

 the minute sanguiferous vessels of these animals ; and the 

 supposed median longitudinal dorsal artery of the hydatina, 

 a more careful examination has shown to be a subcutaneous 

 muscular band. In the extended and active state of the 

 body, a circular cervical plexus of minute transparent vessels 

 is perceptible in several genera of rotifera, as hydatina, oto~ 

 glena, diglena, and notommata, and from this anterior vas- 

 cular network longitudinal vessels appear to communicate 

 with the more symmetrical transverse dorsal arteries of the 

 trunk ; but no motion is seen in these vessels, or in their 

 contained fluid. Vessels also appear to pass from these 



