EARTHWORM PHERETIMA HUPEIENSIS — GRANT 53 



mature individuals give a mean of 562 mg. with a minimum weight of 

 302 mg., and it is between these values that most worms become fully 

 cliteUate. As the semimature and immature categories are con- 

 tinually shifting, it would be difficult to analyze them satisfactorily 

 unless weights were taken at frequent intervals from population 

 samples distributed over a period of several years. Such a project is 

 very important, but would have to be carried out on a more readily 

 available species of worm than P. hupeiensis, which has been sub- 

 jected to routine extermination over its recorded range in the United 

 States. 



Segments: Michaelsen (1895) described P. hupeiensis as having 129 

 segments and again (1899) as having segments ranging in number 

 from 119 to 132. Chen (1933) gives numbers from 110 to 128, and 

 Kobayashi (1938) indicates a range of 97 to 132 for his Korean col- 

 lections. Counts made on preserved material from the Pelham col- 

 lection show no correlation between the degree of sexual maturity and 

 number of segments. The average for 22 juveniles was 125 segments, 

 and for 39 adults it was 126, with a range of 119 to 130 for the entire 

 series studied. 



The whole problem of whether or not earthworms continue adding 

 segments during life has been discussed by Gates (1948). After a 

 study of a number of megascolecid, lumbricid, and glossoscolecid 

 species he concludes that postembryonic growth generally involves 

 the production of new segments, although segment production does 

 not take the same form in every case nor is it uniform throughout 

 the three families. Because no specimen of P. hupeiensis has been 

 found to date that can definitely be regarded as newly hatched, it is 

 impossible to state whether new segments are added after hatching. 

 However, since juveniles and fully mature specimens possess about 

 the same number of segments, few if any additions are made after 

 the worms have attained a length of 35 mm. Careful dissection of 

 juvenile specimens in the region of the anal segment revealed nothing 

 that suggested that this segment was not fully differentiated. 



Setae: The numerous setae, which are weakly sigmoid in shape and 

 about 0.2 mm. in length, are perichaetous, as each segment has an 

 equatorial band of setae passing around it. Michaelsen found 72 

 setae on segment 25, and Chen (1933) gives numbers ranging from 

 68 to 88 for the same segment with 14 to 22 between the spermathecal 

 pores of segment 8 and 10 to 16 between the male pores on segment 18. 

 Gates (1935) records 85 setae on segment 20, and 18 on segment 18 

 between the male pores. 



In the specimens of P. hupeiensis in the Pelham collection, setal 

 numbers averaged about 8 between the spermathecal pores of segment 

 8, with a range from 4 to 13; 12 between the male pores of segment 18, 



