76 



In one lot nine caterpillars were fed from their birth upon leaves 

 Impregnated with the neutral red. The}' ate these leaves without 

 showing any repugnance and developed normally. The general rcnl- 

 dish tint of the body indicated the presence of the coloring matter in 

 the ]>lood. 



For the purpose of avoiding all possibility of soiling the silk the 

 larva? at the beginning of cocoon spinning were carefully washed with 

 a stream of water and carried to freshly collected branches. The silk 

 coming from the spinneret is tinted with rose, and the whole cocoon 

 presents a beautiful red coloration. 



Two caterpillars of this lot were isolated at the fourth molt and 

 nourished during the last age with leaves deprived of the red coloring. 

 These caterpillars faded and the silk which they spun was scarcely 

 tinted with rose. 



Four other caterpillars having eaten natural leaves up to the fourth 

 molt, then received a colored nourishment during the fifth age onl}', 

 and furnished cocoons as red as those of the iirst lot which had absorbed 

 the red during the whole larval life. 



Caterpillars raised upon methjdin blue seemed to eat the leaves with 

 less avidity, their development slower, and they secreted a less abun- 

 dant silk, which was slightly bluish. 



Finally, the last lot of Attacus orizaha^ fed upon leaves washed with 

 a solution of picric acid, gave cocoons with white silk. 



Thus we see that the neutral red passes easily by osmosis through 

 the tissues, while the methylin blue passes through only with difficulty, 

 and the picric acid is completely arrested. In order to reply in the 

 most perfect way to the criticism based upon the hypothesis of the 

 superficial coloration of the silk thread from the possible soiling of 

 the silk, we have taken two caterpillars and injected the neutral red in 

 the next to the last left proleg. These caterpillars were instantly 

 colored with red vvithout appearing in the least incommoded, and spun 

 a slightlv i"osy silL 



(2) Bi>iiihy.r iiiorl. — The same experiments were made upon the two 

 races of Bonihyx morl^ the one with yellow silk and the other with 

 white silk. In the two cases the caterpillars became colored with vio- 

 laceous red innnediately after the tirst meal, and gave a bright orange 

 yellow silk in the tirst case, and a beautiful pure rose for the white 

 race. The color became accentuated according to the duration of the 

 feeding of color food. 



This fact demonstrates that the passage of the coloring matter into 

 the silk gland is less easily made than with Attacu.-i orhaha. Will the 

 result be the same after several generations submitted to this artificial 

 regime? That is what we intend to find out. From these researches 

 the possibility of making a substance coloring matter, for example, 

 pass from the digestive tube to the silk b}' means of the Ijlood, is estab- 



•M 



