144 



The Microscope. 



of fringed plates on the outside of the third and fourth 



pairs of legs."* 



The circulation shows to vastly more advantage 



with the vertebrated animals. Plate VIII. fig. 1, repre- 

 sents the three-spined 

 stickleback, slightly 

 smaller than nature, 

 and fig. 2 represents 

 a portion of its tail-fin 

 when magnified thirty- 

 five diameters. The 

 flat white spaces repre- 

 sent the bones, and it 

 will be observed that in 

 four places the blood- 

 vessels are carried 

 across these in fur- 

 ^ rows excavated as it 

 were in the substance 

 No. 25. Daphnia pnlex, magnified 16 o f t he bone. A vein 

 diameters, b, natural size. 



and artery, placed in 



pairs, may be observed at each side of the bones ; 

 and in some places these may be seen crossing 

 and recrossing each other in a fantastic manner. 

 The arteries may be recognized by their flowing 

 from the heart, and the veins by their flowing 

 towards it, as indicated by the arrows. The narrow 

 vessels connecting the large ones are the capillaries. 



The pale, or rather colourless, appearance of the 

 corpuscles may surprise the observer. The fact is, 



* Baird's "Nat. Hist, of British Entomostraca," 



