BLOOD. 37 



The globose body is inclosed in a coating of loose 

 shapeless jolly, that passes off from one of the lower 

 corners, and forms a short foot-stalk, which nnites M'ith 

 similar foot-stalks from the sister-globnles, and all to- 

 gether are attached to the sea-weed. Each foot-stalk 

 has an organic pore, into which a vessel passes upon 

 the body. 



Yonr attention is first arrested by the breathing sac, 

 M'ith its rows of oblong cells all in wheel-like motion. 

 It is indeed a wonderful object ; but for the present 

 neglect this, as we will i-eturn to it presently, and direct 

 your consideration to the course of the blood. 



It is true tlie fluid which I so name is not red, like 

 that of the Frog w^hicli you have just been gazing at, 

 nor does it carry disks of the same elegantly regular 

 form. But you have the advantage here of tracing, at 

 one view, the whole course of the circulation, from its 

 first rush out of the heart to its return into that organ 



'to" 



again. 



At the bottom of the interior, below the breathing 

 sac, there is an oblong cavity, through w^iose centre 

 there runs a long transparent vessel, formed of a deli- 

 cate membrane, the appearance of which resembles that 

 of a long bag, pointed (but not closed) at either end, 

 and then twisted in some unintelligible manner so as to 

 make three turns. This is the heart ; and within it 

 are seen many minute colourless globules, floating 

 freely in a subtile fluid : this is the nutrient juice of 

 the body, wdiich we may, without much violence, des- 

 ignate the blood. Xow see the circulation of this 

 fluid. The membranous bag gives a spasmodic con- 

 traction at one end, and drives forward the globules 

 contained there ; the contraction in an instant passes on 



