NATURAL HISTORY OF SEVENTEENTH CENT. 243 



a demonstrated fact. Many important details of the structure of 

 various organs were first made known by Malpighi. The micro- 

 scope also enabled him to trace out for the first time something of 

 the anatomy of insects. The silkworm, for example, was carefully 

 observed by Malpighi : he discovered that the small spots which may 

 be seen on each side of the creature are, in reality, carefully-guarded 

 openings into a system of delicate air-tubes, which communicate with 



FIG. 113. SPIRACLE OF SILKWORM. 



every part of the body. These air-tubes, or trachea as they are called, 

 form a respiratory apparatus corresponding with the lungs of higher 

 animals. Fig. 113 shows a view of the breathing aperture, or spiracle y 

 of the silkworm as it appears when magnified under the microscope, 

 and the small circle encloses the object as it appears in actual size. 



FIG. 114. 



FIG. 115. 



Vegetable anatomy next claimed Malpighi's attention for micro- 

 scopic investigation. Unknown to him, DR. NEHEMIAH GREW (1628 

 1711) was also occupied in England with the same investigation, and 

 in 1670 a memoir of Grew's on the subject was read before the Royal 

 Society, and shortly afterwards another paper on the same subject was 

 received from Malpighi. The two observers have agreed in most of 

 the particulars they described, and in the physiological interpretations 

 to be put upon the facts. The fact was stated by both of vegetable 

 structures being composed of cells of various forms, modified from the 

 simplest form of all, shown in Fig. 1 14, in which each cell consists of a 

 little spherical or ovoid bladder of transparent membrane. When the 

 cells are crowded together, as in Fig. 05, the intervening spaces are 

 filled up, and the cells assume a polygonal form. In other circum- 



* 16 2 



