PARTS OF INSECTS, AND MISCELLANEOUS OBJECTS. 141 



globules appear in immense numbers, and in the minute ramifications of the ves- 

 sels, are seen rolling along in single rows, with here and there a white globule 

 scattered among them, not more than half as large as the red oval disks. 



The velocity of the blood is not uniform ; for the current is observed to be 

 subject to sudden momentary checks, after which it a^ain flows on with its for- 

 mer speed. In figure 240, is delineated a portion of the web of a frog's foot, 



Fig. 240. 



magnified three hundred and fifty diameters. The web has the appearance of 

 mosaic work, being divided into beautiful hexagonal figures with a nucleus in 

 the centre of each. The most minute ramifications of the blood-vessels are here 

 seen standing prominently forth, and within them the blood globules are clearly 

 revealed the large oval disks representing the red atoms, and the small round 

 ones the colorless particles. An idea may be gained of the size of the capilla- 

 ries by recollecting the length of the red globules in the blood of the frog. 



POLLEN. The pollen of flowers which appears as a fine dust to the unas- 

 sisted eye, is shown by the microscope to be an assemblage of organized 

 bodies, possessing regular figures, and varying in size, form, and color, according 

 as they are taken from different plants. The color of the pollen is usually yel- 



