ARTICLES 613 



spines, and divided once every 1 1 days. Diversities in the 

 size of the shell and of the mouth and in number of spines 

 were found to be inherited. The 1,277 descendants of one 



Fig. 4. 



" wild " specimen were used to determine whether diverse 

 lines could be isolated by selecting, on the one hand, individuals 

 with a low spine number, and on the other hand those with a 

 high spine number. As a result two diverse lines were obtained 



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Fig. 5. 



(Fig. 6). The average spine number before selection was 

 begun was 2-67 ; that of the high line reached, and maintained 

 after selection was discontinued, an average spine number of 

 2-75 ; whereas that of the low line decreased to 176. Root 

 does not consider the isolation of these heritable diversities 

 as invalidating the " pure-line " hypothesis, since we may 

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