VARIATION IN THE TEETH OF NEREIS. 



MARY HEFFERAN. 



THE purpose of this quantitative study in variation is to 

 determine the modal condition of a character in a species of 

 Nereis commonly found on the west coast of the Atlantic. 

 The material was very generously placed at my disposal by 

 Professor Charles B. Davenport, who collected it during the 

 summer of 1899 at Cold Spring Harbor, Long Island. The 

 animals were found in the sand of the beach and were taken at 

 random, excepting that small ones were rejected. 



These annelids went by the familiar name of Nereis virens, 

 but upon comparing them with Ehlers's ('68, p. 559) descriptions 

 and drawings of that species, I found that although they agreed 

 in most characters, an important difference occurred in the 

 length of the first or postoccipital segment ; that of N. virens 

 being twice as long as the second segment, while that of the 

 Cold Spring Harbor form is about equal to or even slightly 

 less than the second in length. In this character, as also in 

 that of certain parapodal bristles, the " Sichelanhange," which 

 are rather short and broad instead of slender and long as in 

 A r . virens, the Cold Spring Harbor species agreed well with 

 Ehlers's description of A 7 ", limbata, the distribution of which 

 also includes the west Atlantic coast. From these two points, 

 and from the fact that Cold Spring Harbor is slightly south 

 of the southern limit described for N. virens, and within the 

 range of N. limbata, it seems probable that we are here dealing 

 with the latter of Ehlers's two species. It may be possible 

 that the two species overlap in this region at the southern 

 limit of N. virens, and that my collection contained both. 

 However, nothing in the numerical results of my investigation 

 seemed to suggest two distinct or even transitional forms. 



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