122 REPORTS Oif INVESTIGATIONS AND PROJECTS. 



between that of sustained tetanus, which would be caused by unchecked cal- 

 cium, and that of inert relaxation, which would be caused by unchecked mag- 

 nesium. 



In 1906, the writer discovered that circuit-shaped strips of subumbrella 

 tissue of Cassiopea, without nervous centers, will maintain themselves in sus- 

 tained pulsation provided a single contraction be once started in the circuit. 

 This same statement is true of circuit-shaped strips cut out of the heart of the 

 loggerhead turtle. 



Such constantly sustained single waves of pulsation are not observed in 

 nature because the nervous centers which initiate the pulsation-stimulus are 

 so arranged as to mechanically check and annul each wave of pulsation as 

 soon as it has traversed the tissue. There is, then, an interval of complete 

 rest until a chemical change recurs, permitting the nervous centers to send 

 forth a new pulsation-stimulus. Thus there are special devices in nature to 

 prevent the condition of "closed-circuit pulsation" discovered in 1906. 



It is possible that periodic changes in the proportions of calcium and mag- 

 nesium in solution are a contributory cause of each pulsation-stimulus. 



In addition to the research upon pulsation, the writing of a monograph 

 upon the Hydromedusse of the world was completed. This will be illustrated 

 by numerous outline copies of previously described Medusae copied by Mr. Carl 

 Kellner, and also by colored drawings made from life by the writer. 



The annual breeding swarm of the Atlantic palolo came on July 2 and 3 ; 

 and the last quarter of the moon fell on July 2, 1907. Experiments indicate 

 that the worms can swarm when tidal rise and fall is obliterated, but that 

 they can not swarm unless moonlight falls upon the coral rocks within which 

 they live. 



During the year papers embodying the results of researches carried out at 

 the Tortugas Laboratory have been presented for publication by the following 

 authors : 



W. K. Brooks and B. McGlons. The origin of the lung in Ampullaria. 



W. K. Brooks. The pelagic Tunicata of the Gulf Stream, parts 11 and in. 



W. K. Brooks and Carl Kellner. The pelagic Tunicata of the Gulf Stream, part w. 

 A new appendicularian from the Dry Tortugas, with notes on its embryology. 



Edwin G. Conklin. Two peculiar actinian larvae from Tortugas, Florida. 



R. P. CowLES. Habits, reactions, and associations in Ocypoda arenaria. 



C. H. Edmondson. a variety of Anisonema vitrea. 



H. E. Jordan. The relations of the nucleolus to the chromosomes in the primary 

 oocyte of Asterias forbesii. 



Edwin Linton. Helminth fauna of the Dry Tortugas. 



Charles R. Stockard. On the habits, reactions, and mating instincts of the walking- 

 stick, Aplopus mayeri. 



Charles ZelEny. Some internal factors concerned with the regeneration of the chelae 

 of the gulf-weed crab (Portunus sayi). 



A. G. Mayer. Medusae of the world, vol. i, Hydromedusae. 



