The Sexual Phases of Myzostoma. 
By 
William Morton Wlieeler, Ph.D., 
Assistant Professor of Embryology in the University of Chicago, 
Chicago, 111. ü. S. A. 
With Plates 10—12. 
Preface. 
The parasitic geniis Myzostoma, which Fkitz Müller ('85) 
correctly styled »die in Bezug auf ihre Geschlechtsverhältnisse merk- 
würdigste und lehrreichste aller Wurmgattungen«, has been but little 
studied of late. v. Graff, Nansen and Beard have given such a 
full and clear account of the anatomy and sexual phases of these 
highly modified Annelids, that few morphologists would feel inclined 
to enter a field which seems at first sight to promise so little that is 
new and interesting. Nor should I have made this attempt had 
not Prof. Eisig incidentally called my attention to a peculiar Myzo- 
stome, M. pulvinar, of which we had found several specimens while 
on a collecting expedition to the Gulf of Sorrento. A study of this 
and the commoner Mediterranean species [M. cirriferum and M. 
glahrum) led to the following paper, in which I shall attempt to 
give a simpler — and I trust, also — a more satisfactory ex- 
planation of the sexual peculiarities of Myzostoma, than has been 
given by preceding authors. 
For the opportunity of studying at the Naples Zoological Station 
I am indebted to the Smithsonian Institution, and to Prof. Dohrn 
who most generously permitted me to enjoy the Privileges of his 
laboratory after the expiration of the term for which I was ap- 
pointed. I am also indebted to Professors Paul Mayer and Hugo 
Mittheilungen a. d. Zoolog. Station zu Neapel. Bd. 12. 16 
