NOTES ON MEDUS/E 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 larvae 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 Medusae. There are many instances of species such 

 as Gonionemiis murbachii, 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 



