Chaetopterus Variopedatus. 529 



short anal somite to which the growing-zoue is confined. The pos- 

 terior region of the worm is formed by differentiation of this grow- 

 ing-zone. 



The transformation is accomplished by a change of habit. The 

 larva ceases to swim at the surface. It creeps over the bottom where 

 it forms short tunnels the walls of which are made of sand and 

 diatoms cemented together by mucus which is secreted by mucus- 

 cells of the body of the larva. 



The young worm remains permanently confined within one of 

 these tunnels which it eularges as often as may be necessary to accom- 

 modate its own rapid growth. 



The tunnel is enlarged in diameter by being split lengthwise and 

 a new wall is formed in the open space. These tubes are length- 

 ened by the construction of an extension to one end in the form of 

 half of a broad U. Subsequent extensions are made indifferently 

 from one end or other of the base of the old tube. The "intermediate 

 cirm, which is divided from the main portion of the tube by a trans- 

 N'erse septum, becomes macerated and leaves the typical U-shaped 

 tube. 



The tubes are made of mucus which is secreted by the bod}^ and 

 shaped by the anterior region of the worm. The mucus hardens 

 to a parchment-like consistency. 



The rate of growth of the worms is very rapid. Those which 

 develop from eggs laid early in the season reach maturity before the 

 close of the same season. 



Zoological Laboratory, 

 rurilue University, La Fayette, Indiana. 



REFERENCES TO LITERATURE. 



1. Andrews, E. A. Annelids of Beaufort, North Carolina. Proc. U. S. 



Nat. Mus., A^ol. 14. 



2. Beraneck, Edou. Quelques stades larvaires d'un Clietoptere. Rev. 



Suisse de Zool., 1894. 

 ?>. Beyerinck, M. W. Culturversuehe uiit Zoochlorzellen, Liclitereugoni- 



dien und anderen niederen Algen. Bot. Zeitung, Vol. 48, 1890. 

 4. Brandes, G. Die Ursache der Grunfarbung des Darmes von Chsetop- 



terus. Zeit. f. Naturw., Vol. 70, 1898. 



