MISCELLANEOUS. 



Double Cocooning. 



Through all the years of our rearing and in lots representing most 

 of the different races studied the appearance of occasional double 

 cocoons was recorded. By double cocoon is meant a cocoon which is 

 made by the joint labors of two larvae, the one cocoon enclosing the 

 two pupae of these larvae. (See Plate II.) In a few cases triple 

 cocoons, produced by three larvae working together, occurred. This 

 double cocooning habit is of course a familiar one to silkworm growers 

 and there is even a silkworm race aboriginal to the Riu Kui Islands 

 described by Sasaki (Bull. Coll. of Agric, Tokyo Imper. Univer., vol. 

 6, page 33, 1904) in which almost all the cocoons are double. They 

 are large and variable in shape and usually enclose more than two 

 pupae, not rarely even seven or eight. 



Coutagne (Recherches Experimentales sur I'Heredite chez les 

 Vers a Sole, 1902, p. 62 ff ) questions whether an increase or decrease in 

 number of double cocoons in a race is really hereditary, i. e., whether 

 it is an acquired racial character, but inclines to hold it to be a purely 

 ontogenetic character depending upon the amount of space available to 

 the spinning worms. 



But Duseigneur (Monog. du Cocon de Sole, 1875, p. 104) declares 

 that the proportion of double cocoons is in some degree a fairly fixed 

 characteristic of a race. Certain races come up to 30 per cent., in this 

 proportion, while certain others do not get beyond 3 or 4 per cent. 



Lambert (Revue de Viticulture, 1895, pp. 447) reports on a special 

 Chinese race in which in 8 years he was able to reduce the percentage 

 of double cocoons from 15 per cent, to 3 per cent. 



Maillot and Lambert (Traite sur le Ver a Sole, i9o6,pp. 342, ff) 

 in giving the characteristics of many silkworm races regularly give 

 the percentage of double cocoons, this percentage varying from 2 to 

 15, Also in their discussion of the effects and results of crossing they 

 quote cases where the proportion of doubles in hybrid races is less than 

 in either parent race. For example in a hybrid race produced by cross- 

 ing two Chinese parent races the percentum of double cocoons is i in 

 place of 2 per centum or 6 per centum characteristic respectively of the 

 parent races. In other cases the proportion of double cocoons in hybrid 

 races is the same as in one of parent races while in others the propor- 



