MALPIGHIAN TUBES OF BOMBYX MORI L. 203 



In a pupa seven to eight days old, the structures of the cells 

 in the coelomic portion are almost the same as on the preceding 

 day. The lumen is, however, increased in caliber and contains 

 numerous granules (fig. 14). 



In a pupa nine to ten days old, the formation of the common 

 stem is already completed. The cytoplasm is granular and the 

 nuclei are round or ellipsoidal and a thin new intima lies on the 

 surface of the cells facing the lumen. 



In the coelomic portion the cytoplasm contains very many 

 large vacuoles which are situated between the nucleus and the 

 striated border. The ramified nucleus is basal in position and 

 contains some small, highly refractive nucleoli. The chromatin 

 is in the form of small granules or rods, and appears to be arranged 

 surrounding the nucleolus. The striated border is composed of 

 many very fine and closely set striations. The lumen is very 

 irregular in shape, especially in the anterior portion. The 

 process of the excretion is very active, as indicated by the homo- 

 geneous or granular substance filling the lumen and staining 

 light blue with haematoxylin. There are some vacuoles in the 

 excreted substance of the posterior portion. The transparent 

 basement membrane has increased in thickness. 



In a pupa eleven to thirteen days old, the common stem and 

 the coelomic portion remain in the same histological condition 

 as described above. The excretory activity of the cells has 

 increased, and the excreted substance stains deeply blue with 

 haematoxylin as in the larval stage. It need hardly to be 

 mentioned that the imago emerges on the fourteenth or fifteenth 

 day after the pupation. 



4- Malpighian tubes in the imago 



In the imago the common stem opens directly at the junction 

 of the stomach and the intestine, owing to the histolysis of the 

 latter. The common stem is a short narrow tube and measures 

 0.61 mm. in length and 0.17 mm. in width. The epithelium is 

 composed of large flat cells. The cytoplasm is granular and 

 strongly eosinophilous. The nuclei are round or oval. The 



