SEGMENTATION OF CEETAIN POLYCHJITES. 529 



Peculiarities in the Segmentation of certain 

 Polychsetes. 



By 



Florence Bucliaiiaii, B.Sc, 



From the Zoological Laboratory of University College, London. 



With Plate XLII. 



In the last volume of the ' Zeitschr. f. wiss. Zool/ (vol. liv, 

 1892, p. 569) a paper appeared entitled " Ueber Anomalien 

 der Segmentierung bei Auneliden und deren Bedeutung fiir 

 die Tlieorie der Metamerie," by C. J. Cori, dealing chiefly 

 with the intercalation of half- segments, and with cases in 

 which the furrows dividing successive segments externally have 

 become continuous, thus forming a spiral going once, or more 

 than once, round the body of the animal. Cori found seventeen 

 out of about two hundred common earthworms (Lumbricus 

 terrestris) abnormal in one of these two ways. He also 

 found one specimen of a Lumbriconereis, one of Halla 

 parthenopeia, one of Diopatra neapolitana, and one of 

 Hermodice carunculata with intercalated parts of seg- 

 ments. He does not mention, however, how many specimens 

 of each of these species he examined ; and from his account 

 one is naturally inclined to look upon such occurrences as 

 rare, and to call them, with him, abnormalities. It may, 

 therefore, be worth while to point out that there is at least 

 one family of Polychsetes, judging from over eighty specimens 

 coming from different parts of the world, in which cases of 

 intercalation and of spiral segmentation are so common as to 

 be regarded rather as normal individual variations than as 

 abnormalities. This family, from which Cori gives but one 



