EFFECT OF MOISTURE UPON SILK OF HYBRIDS 55 



5. One white cocoon was spun in a damp cell and remained white. 

 Unfortunately it was not possible to breed from the moth which emerged 

 from this cocoon. 



B. Experiments on finished cocoons 

 Cocoons containing larvae 



1. On Jan. 26, at 10 p.m., four pure white, completed cocoons were 

 found together on the net. One was placed in a damp cell, leaving a 

 tiny piece of silk outside in the dry room. The following day at 9 a.m. 

 the cocoon in the box had become brown, whilst the piece outside re- 

 mained white. Of the three cocoons remaining on the net, two were 

 still pure white, but the third had become brownish at the mouth of 

 the cocoon. By 10 p.m. there was no change in the cocoons. The 

 brown cocoon was then placed in a dry cell with CaCl2. When the co- 

 coons were examined on January 28 no change had taken place in the 

 colour. On February 10, on which date the cocoons contained pupae, 

 the cocoons were still the same colour. During March and April, 

 when the moths were being forced to emerge by warmth and damp, 

 the three white cocoons became a pale brown. 



2. A cocoon was white except at one end where it was a pale fawn. 

 It was placed in a damp cell, with the fawn end hanging in the dry room. 

 By the following morning all the cocoon was a dark l^rown except the 

 excluded end. 



3. A cocoon was fawn except a small attachment piece, which was 

 brown; the whole cocoon was placed in a damp cell, and in fourteen days 

 was a dark, dirty brown. 



4. A medium red-brown cocoon was opened, when the interior was 

 found to be a lighter colour than the exterior. This cocoon was placed 

 in a damp cell, and after eleven days had become a deep brown through- 

 out, the inside now being the same colour as the exterior. The orig- 

 inal and subsequent coloration of this cocoon are an interesting demon- 

 stration of the influence of external conditions. 



5. All the white cocoons of F3 generation became various shades of 

 fawn and red-brown when subjected to warmth and moisture. 



The pieces of silk used in these observations, were taken, it 

 will be noted, from, (a), fresh cocoons which contained the larva, 

 (b), cocoons which contained the pupa, and (c), cocoons up to 

 four months old. These experiments all suggest that moisture 

 is a factor of considerable importance in the cocoon colour of 

 this particular hybrid. Moisture, again, would explain the phe- 

 nomenon already noted, that in all cases of cocoons spun in a 

 fresh leaf, the side towards the leaf was always darker, for owing 



