CIRCULATION OF THE BLOOD. 365 



m a large animalcule cage. In page 41 of the second edition 

 of the MicrograpMa Illustrata of the elder Adams,, published 

 in 1747, it is stated that the circulation could be seen in the 

 legs and feet of small spiders and in the legs of bugs ; and the 

 movement of a greenish fluid was also to be observed in the 

 wings of grasshoppers. Leeuwenhoek, he tells us, discovered 

 the circulation in the shrimp and even in the farthest joints 

 of the legs of little crabs, which animals " may be found under 

 brickbats and stones on the shores of the river Thames, when 

 the tide is out ;" unfortunately for the microscopist, these last 

 are no longer to be seen in such localities. The circulation 

 of the blood may be readily viewed in many small fishes ; the 

 older microscopists employed the eel, the carp, the gudgeon, 

 and the flounder, for the purpose of exhibiting it ; these were 

 either conflned in the fish-pan, or placed with water in small 

 glass tubes; but the fish now commonly used is the Stickle- 

 back, Gasterosteus. Flounders, when sufiiciently small, form 

 very beautiful objects, but are much more rarely met with 

 than the stickleback, which is abundant in most ponds and 

 ditches. Amongst the reptiles, the newt and frog, and the 

 tadpoles of each, are generally employed; in the former the 

 circulation may be viewed in the tail, in the feet, and in 

 the branchiaj, whilst in the latter the web of the foot, the 

 tongue, and the branchi* and tail in the tadpole, are the parts 

 which exhibit it to the best advantage. In the mammalian 

 class, it can be seen in the wing of the bat and ear of the 

 mouse, and in other parts not too opaque. In some ofi^e 

 invertebrate animals, it will be noticed that, although the 

 blood itself is of a red colour, still its discs or corpuscles 

 are white, the colour, unlike that in the vertebrate series, 

 being due to the fluid in which the corpuscles float, and not 

 to the corpuscles themselves. 



Method of Viewing the Circulation in the Vertebrata. — The 

 tadpoles of the newt, frog, and toad, when about to be 

 examined, must be placed either in a large animalcule cage, 

 or in the trough described at page 142, where they may be 

 subjected, if necessary, to slight pressure. The larva of the 

 newt, when about an inch in length, with the ' branchiaj 



