58 INHERITANCE IN SILKWORMS^ I 



(No, 415) One hundred and forty- four larvae all with clouded 

 heads. 



Matings were made in 1907 from this material and will be reared 

 this spring (1908). 



Congenitally "hornless" larva. — Various matings were made in 

 several years (inbred matings from first generation hybrids also mated 

 for second generation rearings) of moths derived from larvae born 

 without the caudal horn or with it in greatly reduced condition (PI. I, 

 fig. 12), The results of all these matings show that the character is not 

 heritable. That is, does not behave as a Mendelian or alternative char- 

 acter, nor can it be fostered and fixed by selection. 



Experimentally "dehorned" larvce. — The horn seems to be a use- 

 less structure. It is not an organ of defense, neither secreting an imi- 

 tating or a mal-odorous fluid nor can it pierce or wound in any way an 

 enemy. Besides, for nearly 5,000 years the silkworm has had no enemy 

 except disease germs to defend itself against. This fact of the apparent 

 present uselessness of the horn and the fact that it not infrequently 

 appears in rudimentary condition or is even wholly wanting suggested 

 the experimental mutilation of silkworm by removing this degenerating 

 structure. Would such mutilations or removal of a structure already 

 tending congenitally to degeneration or loss be more likely to be in- 

 herited as an "acquired character" than other mutilations such 

 as have been brought about by experiment or custom and have shown no 

 signs of being handed down to the young. 



Considerable work was done during three successive years in test- 

 ing this. In no case was there any indication of the transmission by 

 inheritance of the mutilation. So this case may join the many others 

 all of which (almost without question) have been repetitions of the 

 same evidence of negation. 



Sport wing pattern of moths. — In the seven years of rearings sev- 

 eral well-marked sport variants of the wing pattern have appeared. 

 Various matings to test the behavior in inheritance of these sports were 

 made. For example, in 1905 two matings were made of a sport wing 

 pattern with a normal wing pattern. In the first or hybrid generation 

 there was no reappearance of the variant pattern. In rearings (1907) 

 from inbreds from this hybrid (1906) generation there was also no 

 reappearance of the sport pattern. 



These pattern sports are various in character, some of them being 

 asymmetries, some extreme emphasis of the normal faint pattern- 

 ing, some the appearance of large conspicuous well delimited black 



