EXPERIMENTS, ON THE CONTROL OF ASYMMETRY 
IN THE DEVELOPMENT OF THE SERPULID, 
HYDROIDES DIANTHUS! 
CHARLES ZELENY 
SEVEN FIGURES 
INTRODUCTION 
The following experiments? were made as part of a study of 
the factors controlling asymmetry in the Serpulid, Hydroides 
dianthus. The operations were performed on young individuals 
in which asymmetry was just starting to develop and in which the 
adult mechanism for reversal of the opercula was not yet present. 
The results are interesting not only in connection with the prob- 
lem of the cause of the original asymmetry and of the reversal 
of the opercula in adults but also as bearing on the extent of agree- 
ment between regeneratory and ontogenetic stages. A more 
definite formulation of the problems follows. 
1. The first functional operculum of young animals is developed 
before the first rudimentary operculum. In the absence of any 
special mechanism in the form of a rudimentary operculum does 
reversal of position follow removal of the fanctional organ at this 
stage? What bearing does the behavior following such opera- 
tions have on the question of the origin of the original asymmetry 
and the cause of reversal of the opercula in adults? 
2. The first functional operculum of the young is different in 
type from that of the adult. Does the regenerated operculum 
1 Contributions from the Zoological Laboratory of the University of Illinois, 
No. 8. 
2 The experiments were performed at the Biological Laboratory of the Bureau 
of Fisheries at Woods Hole, Mass., during July and August, 1909. Iam indebted 
to Dr. Francis B. Sumner, the director, and to Professor Raymond C. Osburn, 
acting director during a part of my stay, for many courtesies. A preliminary 
report of the experiments was given before the Central Branch of the American 
Society of Zoologists at the lowa City meeting, April 8, 1910. 
927 
