196 HIROWO ITO 



definitive organ, the remaining portion disappearing entirely. 

 In Bombyx mori Ikeda ('13) has described a mode of develop- 

 ment very similar to that described by Cholodkovsk3\ 



The present study vras undertaken to ascertain definiteh' 

 in what manner the metamorphosis of the malpighian tubes 

 takes place in the silkworm, and I was fortunate enough to 

 obtain some results which have not hitherto been recorded regard- 

 ing the following points: a) the histolysis of the urinary bladder; 

 h) the histolysis and histogenesis of the common stem, and 

 c) the histolysis of the portion of the malphigian tubes enclosed 

 in the walls of the rectum, 'included portion.' 



MATERIAL AND METHODS 



The material for the present studj^ was obtained from the 

 univoltine race of Bombyx mori, known in Japan as 'Awojiku.' 

 The larvae were fixed either in Perenyi's fluid or in sublimate 

 alcohol warmed to about 80°C. For the pupae various fixing 

 reagents were used. The best results were obtained with picro- 

 sulphuric acid and Perenyi's fluid. The material was embedded 

 in paraffin. The sections were cut from 5 to 10^ in thickness 

 and were stained with Delafield's haematoxylin, picrofuchsin, 

 and various other combinations of stains. 



OBSERVATIONS 



1. Malpighia7i tubes in larvae 



The malpighian tubes are situated near the posterior part of 

 the body, opening into the ventrolateral side of the alimentarj- 

 canal just at the junction of the small intestine and the colon. 

 The tubes are six in number, three on each side. Two tubes 

 first unite into one and then the third one fuses with the other 

 two. The common stem of the three tubes is connected with the 

 urinary bladder. This organ opens directly into the alimentary 

 canal. Each malpighian tube runs at first forward as far as the 

 anterior edge of the sixth or seventh segment, along the dorso- 

 lateral side of the stomach. Then it turns on itself and goes 

 backward a little bej^ond the colon, where it makes irregular 



