EISAKU IIZUKA and QIULIAN LI*, : Properties of a Chinese domestic silk, Jin Lin, in relation to the sex of the silkworms The physical properties were compared between threads spun by male silkworms and those spun by female silkworms with cocoons produced by Jin Lin,one of the typical Bombyx mori varieties in Sichuan, China. The size of the thread changes gradually along the whole length of the thread. The physical prorerties of the thread such as dynamic elastic modulus, tenacity, elongation,

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... gree of crystallinity and density showed linear relation with the size of the thread, suggesting that the physical properties as a whole can be estimated from data of several specimens taken at regular intervals along the whole length. The correlation was negative except for the elongation. A similar correlation was observed also in each of the sample populations collected from a specified portion of the cocoon layer, irrespectiveof the portion. This linear correlation was attributed to the spinning mechanism peculiar to the silk thread. The values of the dynamic elastic modulus and the degree of crystallinity were somewhat higher in the female thread than in the male thread when the mean values were compared; the differences became moree pronounced when the values estimated from regression lines for the same thread size were compared. Besides, the tenacity and the density became significantly larger in the female thread when the difference in the mean thread size was considered. These facts strongly suggestthat the crystalline structure is more advanced in the female thread than in the male thread when the thread size is similor.