A COMPARISON OF THE SENSE-ORGANS IN MEDUSAE 
OF THE FAMILY PELAGIDAE 
ROBERT PAYNE BIGELOW 
Instructor in Biology and Librarian, Massachusetts Institute of Technology 
THIRTY-EIGHT FIGURES 
The work to be described in the following pages was done at 
the suggestion and under the supervision of Professor Brooks 
at Baltimore during the winters of 1888-89 and 1889-90 and dur- 
ing the summer of 1889 in the Fish Commission Laboratory at 
Woods Hole, where that summer Professor Brooks was director 
of the Laboratory and I the proud holder of the university table 
— my first appointment. The manuscript and illustrations were 
completed and handed to Professor Brooks in November, 1890, 
with the intention that the paper should form a part of the mono- 
graph on the medusae that he then was planning. That book 
has not been published. 
The point of view from which this paper was written is exhibited 
in the following sentences quoted from the opening paragraph of 
the manuscript of 1890: " In his System der Medusen (p. 504) 
Haeckel says, 'The genera Ephyra, Palephyra, Zonephyra, 
Pelagia, and Chrysaora form five steps in a connected phyloge- 
netic process of development w^hich is repeated at the present time 
in the ontogeny of Chrysaora according to the fundamental 
law of biogenesis.' As indicated in my preliminary paper (1890), 
Dr. Brooks has pointed out that Dactylometra should be added 
to the series as the final form, and that, so far as the development 
