124 EXPEDITION OF THE "ALBATROSS," 1S99-1900. 



are sinistral and 46 per cent dextral; while in Hamiita valley 69 per cent 

 are sinistral and 31 per cent dextral. We see, then, that the snails 

 gradually change from dextral to sinistral as we pass from Tipajrui to 

 Pirae valley. 



Two hundred and eight snails of the type represented in Figs. 3 and 8 

 were collected in the four valleys, and 96 of them contained 150 young. 

 71 per cent of these young snails were of a light horny-yellow color very 

 similar to that of the parent snail ; 10 per cent, however, were slightly 

 lighter than the parent, and 19 per cent were considerably darker in color 

 than the shell from which they were dissected, and resembled the normal 

 yoving obtained from snails represented by Fig. 5. Turning to the color- 

 type represented in Fig. 5, we find that out of 255 individuals collected 

 in Tipasrui, Fautaua, Hamuta, and Piraj valleys, 119 contained 198 young. 

 Of these young snails 55 per cent were very similar in color to the adults 

 from which they were dissected, 40 per cent were lighter in color and 

 resembled the normal young of the color type shown in Figs. 3 and 8, 

 while 5 per cent were slightly darker than the parent shell. It is evident, 

 therefore, that Figs. 3, 5, and 8 represent mere color sports of one and the 

 same species of snail, for the young intergrade freely. 



In Tipcerui valley all of these young snails are dextral, while in PirJB 

 they are all sinistral, exactly as are the adults in the respective valleys. 

 In Fautaua valley, however, 54 per cent of the adults and 55.5 per cent of 

 the young are sinistral ; while in Hamnta, which lies between Fautaua and 

 Pira? valleys, 69 per cent of the adults and 73 per cent of the young are 

 sinistral. The small discrepancies between the percentages of sinistral 

 adults and their sinistral young are probably due to aberrations of chance 

 caused by the smallness of the number of snails observed, and would per- 

 haps tend to disappear were a larger number to be studied. 



It is interesting to observe that in Fautaua valley the dextral adults 

 give 60 per cent dextral and 40 per cent sinistral young; while the 

 sinistral adults of the same valley give 68 per cent sinistral and 32 per 

 cent of dextral young. Also in Ilamuta valley the dextral adults give 

 66.6 per cent dextral and 33.3 per cent .sinistral young; while the sinistral 

 adults give 95.5 per cent sinistral and 4.5 per cent dextral young. We see 



