DEPARTMENT OF MARINE BIOLOGY. 1 53 



As a practical result it is found that a ^-molecular solution of MgCla or 

 MgSOi is a valuable fluid for stupefying marine animals, enabling one to kill 

 them after treatment in the magnesium in a completely uncontracted state. 

 There is, however, such great diversity in the reactions of motile plants to 

 these ions that the above hypothesis must be advanced with caution, merely 

 as a possibility. 



Another result is that if a contraction wave be once started in any one 

 direction in a ring-shaped strip of any tissue capable of pulsation, the wave 

 will continue traveling around and around the circuit until interfered with and 

 annulled by a wave coming in the opposite direction. This applies to the 

 vertebrate heart as well as to the medusa, and the experiment enables us to 

 study the phenomena of transmission independent of recurrent stimulation. 



In conclusion, we may say that the success of the efforts of those who have 

 come to study at the Tortugas appears to justify the policy which the Labo- 

 ratory has pursued in choosing certain gifted men for its guests each season, 

 rather than throwing open its doors to general applicants. In our enlight- 

 ened land those whose studies lead to the discovery of laws of nature do not 

 long remain unappreciated and unknown, but our national effort is happily 

 directed to discover such as soon as possible among the rising generation. 



A very large proportion of young men of promise have been invited to 

 study at Tortugas in the confident hope that the encouragement which it is the 

 Laboratory's privilege to accord them will result in the advancement of 

 science. And thus at the conclusion of these first five years of its history it 

 is my happy privilege heartily to thank those who have been my companions, 

 for the honor they have done the Laboratory through their achievements in 

 science, and for the courage and devotion which they have displayed in the 

 prosecution of their work. To the crew of the Physalia, who have cheerfully 

 stood by their posts in times of danger and hardship and unfailingly per- 

 formed their duties, I wish to express my appreciation of their fidelity and 

 courage. 



