SENSE-ORGANS IN MEDUSAE 
753 
tion ('95) of the sense-organs of Rhizostoma, in connection with 
which he refers to special points in the anatomy of these organs in 
Cotylorhiza; by Vanhoffen's ('02) descriptions and figures of the 
sense-organs of Atolla, Periphylla, Sanderia, and Dactylometra 
Africana; and by my account ('00) of the development of the 
rhopalia by metamorphosis of the larval tentacles in Cassiopea. 
Vanhoffen's description of the sense-organs of Dactylometra is 
very brief, and neither he nor Hesse mentions the peculiar pitted 
lateral pockets that I find in the sensory niche of Chrysaora and 
Dactylometra, although Hesse finds in Rhizostoma a thickened 
area of sensory epithelium in a similar postition, thus confirm- 
ing Elmer's earlier observation. 
In the following pages reference to the work of other investi- 
gators will be made as occasion may arise. For a general histor- 
ical review of the subject the reader is referred to the admirable 
summaries given by the brothers Hertwig ('78) and von Lenden- 
feld ('82) and later by Hesse ('95). 
The material for this investigation consisted for the most part 
of preserved specimens furnished by Dr. Brooks including some 
young stages of Chrysaora collected by Professor F. S. Lee. I 
am indebted to Mr. Austin Gary for some young material of 
Dactylometra collected, I think, at Newport. In view of Mayer's 
observations it should be noted that when reference is made to 
Chrysaora the form found in the Chesapeake Bay is meant, and 
the name Dactylometra is used for the form found in the open 
sea. 
In the series Palephyra, Pelagia, Chrysaora, Dactylometra, 
and Kuragea, as generally understood, we have a series of medusae 
of similar form and structure. In all the umbrella is relatively 
flat and is provided at its margin with eight sensory clubs, or 
rhopalia, four perradial and four interradial. 
These genera may be distinguished briefly as follows. Pale- 
phyra has 8 tentacles, 16 marginal lappets and in the stomach 
are four interradial septal nodes, homologous with the septa of 
the scyphistoma larva (Bigelow, '00). An account of the pos- 
session of these septal nodes Palephrya is taken by Vanhoffen 
('91) from Haeckel's order Discomedusae and placed with the 
