120 REPORTS ON INVESTIGATIONS AND PROJECTS. 



fied Atherinas were temporarily protected from the gray snapper. Most of 

 these experiments need to be repeated, and all of them need to be extended. 

 They indicate warning color as psychologically possible, but they by no mean? 

 prove that it exists. 



To test the latter question as many of the reef-fish as could be obtained 

 were thrown living to the snappers, and all the species without exception 

 were taken. There was no hesitation except in the case of some specimens 

 of Chylomycterus. The following species were available, most of them in 

 numerous individuals : Abudefduf marginatus, Apogon sellicauda, Chylomyc- 

 terus schoepA, Haemulon flavolineatum, Iridio bivittatus, Neomaenis griseus 

 juv., Pomacentrus leucostictns (in all its color variations), Tliahassoma 

 bifasciatum, Thalassoma nitidum. These species, although few in number, 

 show a considerable variety of brilliant colors and numerous color patterns 

 all wholly familiar to the gray snapper. Feeding experiments of this sort 

 should be extended to include all the fishes of the reefs. The fish must be 

 liberated among the snappers. If offered as bait on a hook attached to a 

 line they are commonly refused, and the impression may thus arise that 

 the fish are warningly colored. 



The conditions at the Tortugas are peculiarly favorable for the work of the 

 sort here outlined. The water is very clear and nearly always quiet, the reefs 

 lie at the door of the laboratory ; the fish occur in great variety and abundance ; 

 there is no commercial fishing. Here, if anywhere, should one be able to study 

 many biological problems by working at fish while they are in their natural 

 environment and under no restraint, and by checking the results thus obtained 

 in a suitably equipped laboratory immediately at hand. 



Alfred G. Mayer studied the rhythmical pulsation of Scyphome- 

 dusae and the nature of the response of the Atlantic palolo, which 

 swarms each year within three days of the last quarter of the July 

 moon. Drawings were also made of all new or interesting Medusa? 

 previous to the arrival of Prof. Henry F. Perkins, who then took 

 up the study of the Medusae. 



Preliminary Report of Alfred G. Mayer upon the Rhythmical Pulsa- 

 tion of Scyphomedusae {Tortugas Laboratory, 

 April-August, 1905). 



If we cut off the marginal sense-organs of the scyphomedusa Cassiopea, 

 the disk* becomes paralyzed and does not pulsate in sea-water. The disk 

 will pulsate in sea- water, however, if we make a series of concentric, broken- 

 ring-like cuts through the muscular tissue of the sub-umbrella. Then upon 

 momentarily stimulating the disk, in any manner, it suddenly springs into 

 rapid, rhythmical pulsation so regular and sustained as to recall the move- 

 ment of clock-work. 



It is not necessary that the cuts through the sub-umbrella tissue of the 

 disk be concentric circles, for any shape will pulsate which allows contrac- 



*In this report the term "disk" will be used to designate Medusae from 

 which the marginal sense-organs have been excised, while the term "Medusa" 

 will designate the normal perfect animal. 



