MALPIGHIAN TUBES OF BOMBYX MORI L. 199 



be said that the more wavy it becomes, the larger folds in both 

 the inner and outer spaces of the peritoneum. They thus sur- 

 round ahnost completely the epithelium of the rectum. Both 

 the cells and nuclei of the tubes in the rectal wall are very much 

 smaller than those of the coelomic portion of the tubes. The 

 epithelium is composed of very flat cells, especially in the outer 

 space of the peritoneum. The cytoplasm is either homogeneous 

 or granular in structure. The nuclei are also ramified, and densely 

 chromatic, with small darkly stained chromatin granules. The 

 striated border is not well developed in this region, but doubtless 

 it is always present, at least in a feebly developed condition, 

 even in the cases in which it is not visible. The lumen is nar- 

 rower than that of the preceding region and contains some 

 excreted granules which stain deeply with eosin. 



■2. Malpighian tubes in the prepiipal stage 



The urinarjr bladder has become considerably reduced in 

 diameter, measuring about 0.58 mm. by 0.25 mm. The cyto- 

 plasm has become vacuolated, and is gradually disappearing. 

 The nuclei of the component cells have united to form a mass 

 which stains deeply with haematoxylin. The intima is now 

 separated from the cells and occurs shrunken in the lumen. 

 The basement membrane is clearly defined, owing to the vacuo- 

 lation of the cytoplasm, and is granular in structure. The 

 muscles are also on the way to histolysis. The sarcolemma 

 shrinks and is attacked by the phagocytes, and at the same time 

 the striation disappears, as is the case with histolysis of the 

 intestinal muscles. Finally, the muscular substance completely 

 disappears, leaving behind some nuclei here and there. 



In the common stem, just the same process of disintegration 

 takes place as in the urinary bladder. The imaginal cells are 

 greatly increased in number and size. The nucleus is round or 

 ellipsoidal and contains many fine chromatin granules. 



The coelomic portion comes in contact with the alimentary 

 canal, which by this time has become very much flattened and 

 contracted, owing to the digestion and excretion of the contents. 



