196 



AGRICULTURE AND FORESTRY. 



The quantitative changes of the live and dry zueight of the silk- 

 worm during its development} 



1000 specimens of the Japanese white-spinner g 



ave : — 



Just hatched .... 

 I. Period, after 175 hours 

 159 » 



2. Period 



3. Period, „ 



4. Period, „ 



5. period, „ 

 Empty cocoon 

 Pupa alone . . . 

 Cocoon with pupa 

 Butterfly. . . . 



150 



165 

 177 



Live weight 



g. 



0-414 



4734 



25-57 



1 14-05 



514-17 



2,220-99 



140-00 



1,03000 



1,170-00 



503'56 



Dry weight 



0-098 

 0-752 

 3-662 

 14-92 

 62-69 

 436-85 

 I22'50 



2i7'4i 

 339'9i 

 142-17 



Relation of 

 the Live 

 Weight. 



Relation of 

 the Dry 

 Weight. 



The weight of the worm 

 when just hatched = i. 



I* 



1 1-4 

 61-8 



275-5 

 1,241-9 

 5,3647 



2,826-1 

 1,215-0 



ri 



37-4 



T52-2 



6397 

 4,457-7 



3,468-5 

 1,4507 (?) 



The increase in the weight of the silkworms is thus quite enor- 

 mous, especially after the fourth casting. When ready to spin, they 

 have increased their live weight nearly 5,400-fold, and that too 

 within 34 days 10 hours, the total period of development. Whereas 

 it takes 2,415 of the newly hatched grubs to make a gramme, a 

 single one ready to spin weighs 222 gr. 



Before it begins to spin, the silkworm loses its appetite, crawls 

 about restlessly, often raising its body like a sphinx, empties itself 

 of excrements, and becomes noticeably translucent. The greatest 

 change, however, is internal. The two spinning-glands — long, 

 coiled conduits, lying on either side of the alimentary canal — 

 have become gradually filled with transparent, thick, fluid silk- 

 stufif, which comes forth from them, when the silkworm begins 

 to spin, through the so-called spinning-teats in its head, stiffening 

 in two separate threads. These threads, however, become instantly 

 cemented together in a double thread in the short duct common 

 to both, in consequence of their coating of glue. The length of 

 this double thread varies between 350 and 650 meters in different 

 breeds and cocoons, according to their abundance of silk.^ 



^ After Kellner, in " Landvvirthschafd. Versuchsstationen von Nobbe." Bd. 

 XXX., p. 75, 1884. 



2 Strong silk-threads with the appearance of violin-strings are known in 

 commerce by the Japanese name Tengiisuj EngHsh, silkworm-gut ; French, yf/*-/^ 

 Flore?ice. In China they are made directly from the spinning-glands of full- 

 grown silkworms, and have for some time been used with us for surgical 

 sewing-thread, and also in large quantity for fishing-lines. (See also Caligula 

 iaponica^ Butl.) 



