54 



MICROSCOPIC OBJECTS. 



seen in fig. 3 (p. 55) , which is a magnified drawing of a por- 

 tion taken from the part b. This exquisite microscopic 

 structure is the same even in its most minute ramifica- 

 tions. 



In the formation of the spiraculse it is desirable to ren- 

 der the entrance of air as free as possible, but to prevent 



Fig.\. Fig. 2. 



the admission of any particles of foreign matter ; and 

 these objects are effected by the mechanism represented 

 in fig. 4, which is a highly magnified view of the small 

 oval apertures seen along each side of fig. 2. 



In aquatic creatures the above arrangement of the 



