XX COLOR PATTERNS. 



lated, marbled or mottled pattern. This is a line of pattern 

 evolution peculiar to Partulina, at its acme in such species as 

 P. proximo, and the Perdicellas, decadent in many Partulinas 

 and Newcombias. 



In Achatinella the streaks, when present, are not sharply 

 defined and always run in harmony with growth-lines. 



The spiral bands of Achatinellidcc belong to two band- 

 systems, entirely separate in inheritance. The genesis of 

 the irregularly placed bands is readily traceable in existing 

 species, but the origin of those of the four-band pattern is 

 unknown. 



Irregularly placed bands. Many species which have spiral 

 bands in the adult stage, are streaked when young. The 

 several stages from the streaked to the banded pattern char- 

 acterize various races or species ; so that it appears likely 

 that the continuous-banded pattern was never produced by 

 a single mutation from the streaked, but by a series of pro- 

 gressive or orthogenetic mutations. The sequence seems to 

 be somewhat thus: 



(a) longitudinally streaked (pi. 60, figs. 4&-4c). 



(b) streaks cut by light spiral lines or bands, leaving 

 streaked zones or spotted spiral lines (pi. 60, f. 6; pi. 

 56, f. 56). 



(c) color of the dark zones or bands intensified or diffused, 

 losing the streaked or spotted pattern (pi. 56, f. 5e, 5/). 



Many individuals are intermediate between a and b, or b 

 and c. Often instead of several or many pale or white bands 

 appearing, the upper half of each whorl loses the streaked pat- 

 tern, leaving it on the portion below the periphery, producing 

 a bicolored pattern of cuticle, as in pi. 57, figs. 2&, 15. This 

 is merely a special modification of stages b or c. 



Judging from its sporadic occurrence, albinism may ap- 

 pear as a mutation at any stage of pattern-evolution; melan- 

 ism is perhaps more frequent in the later stages. 



All stages from streaked to banded may be seen in some 

 species, such as Achatinella fulgens and Partulina redfieldi. 

 May species remain in the primitive stage, while in others 

 only the terminal pattern is seen. 



