480 Howard Edwin Enders. 



The i^resence of hundreds of Spiocliwtopterus larvae, which, in the 

 younger stages, resemble the younger larvae of Chsetopterus, confused 

 me for two weeks until I permitted several of each genus to settle 

 down and complete their transformation. When this was completed 

 I discovered that the majority of the transformed individuals were 

 Spiochsetopterus. 



The fertilization and segmentation of the egg has been described 

 by Mead, and the free swimming young have been described by 

 Wilson, therefore these subjects will be passed over briefly. My OAvn 

 description will have reference to the transformation and development 

 up to the period at which the definitive characters of the adult form 

 have begun to appear. In order to properly interpret the transforma- 

 tion I shall take up the adult morphology before dealing with the 

 embryology. 



In my study of the adult worms I have verified J. Joyeux-Laffuie's 

 monograph on Chsetopterus but will here describe chiefly such parts 

 as will aid in understanding the transformation of the larva. 

 Throughout the paper I have usually used Laffuie's nomenclature for 

 the adult and also for the larva. 



The work, of which the present paper is an account, has been 

 carried on in the Zoological Laboratory of the Johns Hopkins Uni- 

 versity, and in the Fisheries Laboratory at Beaufort, l^orth Carolina. 



I am indebted to Honorable George M. Bowers, United States 

 Commissioner of Fish and Fisheries, for the privilege of occupying 

 a table in the Fisheries Laboratory at Beaufort, ISTorth Carolina, and 

 to Dr. Caswell Grave, Director of the Laboratory, for many privileges 

 extended. To Dr. E. A. Andrews, of the Johns Hopkins University, 

 I am indebted for valuable suggestions in the work. I desire to 

 express my thanks to Mr. Charles Hatsell of Beaufort, ISTorth Caro- 

 lina, for specimens of living Chsetoptems, which he collected and 

 sent me during the winter of 1905. 



To Professor Brooks I express my hearty appreciation of his 

 interest and friendly counsel in the direction of my work. 



Chwtopterus variopedatns, Ren. et Clapd., is a widely distributed 

 tubiculous annelid of the family Chsetopteridse. The individuals 

 of each country and of widely distributed areas in Europe were 



