102 
tubes or tracheae). Note that these branch and 
ramify upon the surface of the mid-gut and malpighian 
tubes (Fig. 39). 
2. Large muscular fibres, together with elastic 
fibres, forming a meshwork. Note that they are 
circular and longitudinal (external). Note that at 
the edge of the viscus they are seen in optical section 
(Fig- 39 )- 
3. Large cells with large nuclei and granular 
protoplasm (epithelium of mid-gut). Note some in 
Fig. 39. Microscopic appearance of Mid-gut, shewing Cell 
Structure and Zygotes 
situ forming a single layer of polygonal epithelium? 
and others detached and in process of being carried 
along by fluid streaming from interior of mid-gut. 
Note that in some places these cells are undergoing 
vacuolisation with dancing of the protoplasm granules 
(Fig- 39 )- 
