NOTES ON MEDUSAE OF THE WESTERN ATLANTIC. 
By H. F. PERKINS. 
The Marine Biological Laboratory of the Carnegie Institution of Wash- 
ington in the Dry Tortugas is admirably situated for the study of many of 
the lower marine animals, their behavior, and the conditions of life, and in 
none of the great groups are there better opportunities than in the Ccelen- 
terates. In addition to the conditions ordinarily found in a region of coral 
reefs and coral islands, one quite unique feature occurs in the Tortugas in 
the presence of the old fortification and surrounding moat which occupy 
the entire surface of the islet known as Garden Key. This ruined structure, 
Fort Jefferson, dates back to the days of cast-iron cannon and _ vertical- 
walled forts of brick. The moat affords remarkably favorable conditions 
for the growth and multiplication of the lower forms of plants and animals, 
sheltered as it is from the violence of storms by the sea-wall, its shallow 
water warmed by the fierce rays of the sun and kept from stagnation by the 
agitation and partial change of the tides. Thus an unusual set of conditions 
obtains, and many of the minute forms which are daily swept in by the tide 
must find this an ideal place to grow and increase and become permanently 
established as part of the population of the moat. 
Another fortunate circumstance is the ease with which cultures of eggs 
and larvz may be maintained at the laboratory, the water in the culture-jars 
being cooler than that in the surrounding sea and considerably cooler than 
that in the moat. The distance of 4 miles separating the two islets occupied 
by the fort and by the laboratory is made less of a difficulty by the use of 
the laboratory launch, which makes it possible to transfer material from the 
moat to the aquaria at Loggerhead Key with little delay. 
The writer has for several years been interested in the causes of migra- 
tion and segregation of Meduse. There are many instances of species such 
as Gonionemus murbachu, of Woods Hole, which have become established 
in some locality of very limited extent, and at a great distance from the 
nearest allied species. The circumstances which have caused first the distri- 
bution and then the segregation of the form offer fascinating fields for study 
and speculation. A particularly interesting phase of the problem is offered 
by the special adhesive organs which occur in several of the species which 
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