574 THE AMERICAN NATURALIST. 
which take place in the formative segment and tend to restore 
it to the normal. 
In conclusion I wish to express my thanks to Professor 
E. L. Mark for most helpful suggestion and criticism. 
CAMBRIDGE, Mass., May 24, 19o1. 
LITERATURE. 
ANDREWS, E. A. 
92. Bifurcated Annelids. Amer. Nat. Vol. xxvi, pp. 725-733- 
ANDREWS, E. A 
'904. Some Abnormal Annelids. Quart. Jour. Micr. Sct. Vol. xxxvi, 
pp. 435-460. Pls. XXXII-XXXIV 
BELL, P. J. 
'87. Note on a Bifid Nereis pelagica. Proc. Zoöl. Soc. London. 1887, 
p. 
BuLow, C. 
'83. Ueber Theilungs- und hee an eet bei Würmern. 
Arch. A Naturg. Jahrg. 49, Bd. i, pp. 1-96. 
M’InTosH, W. 
’85. Report on ie Annelida Polychaeta. Challenger Reports, Zoology. 
Vol. xii, pp. 198-205. Pl. XXXI. 
RAND, H W: 
'98. Regeneration and Regulation in Hydra viridis. Arch. f. Entwick- 
elungsmechanik. Bd. viii, Heft i, pp. 1-34. Pls. I-IV. 
RAND, H. W. 
'99. The Regulation of Graft Abnormalities in Hydra. Arch. f. Ent 
wickelungsmechanik. Bd. ix, Heft ii, pp. 161-214. Pls. yay 
ROBERTSON, C. 
'67. Note on a Double Faken Lumbricus terrestris. Quart Jour. 
Micr. Sci. Vol. vii, pp. 157-158. Two figures. 
