290 University of California Pulilicafious in Zoology [Vol. IS 



4. No amount of hydrographic change or of variation in viscocity 

 of the water can explain the observed differentials. 



5. Solitary forms show an increasing preference, so to speak, for 

 the surface, as the temperature of the surface water increases from 

 16°C to 20°C ; while aggregate forms show a similar preference as the 

 temperature decreases. 



6. The chain of aggregate forms remains attached to the solitary 

 salpa after having been liberated from its mantle cavity into the 

 water. 



7. One solitary form is carried into cold surface water by virtue 

 of the combined locomotive power of the aggregate forms in each long 

 protruding chain, while sJiort chains are carried into warm surface 

 water by virtue of the locomotive power of the attached solitary form. 



8. Owing to the strain due to the opposite direction of locomotion 

 of solitary form and of attached aggregate forms, the protruding 

 chain becomes detached from the stolon periodically, i.e., at the ' ' inter- 

 mediate piece ' ' before an entire ' ' block ' ' of aggregate forms has been 

 protruded. 



9. Contrary to the prevailing plankton concept, Salpa democratica, 

 a typical plankton organism, controls to a significant extent its own 

 distribution just as certainly as does any fish or other animal com- 

 monly included under the term of nekton. 



It is unnecessary to state that the sixth, seventh, and eighth con- 

 clusions, while apparently unescapable, are all based upon indirect 

 evidence and must be regarded as tentative rather than as fully estab- 

 lished. In conclusion, if this paper serves to stimulate a closer 

 morpho-physiological scrutiny of the life cycle of the Salpae, if it 

 serves to instigate a closer study of their habits, if it serves to rectify 

 a prevailing misconception concerning plankton distribution, and if 

 it serves as an antitoxin against the too prevalent tendency of morph- 

 ologists to ignore the ecologist's point of view and of ecologists to 

 ignore the morphologist 's point of view, its primary aim will be 

 accomplished. 



Transmitted July 10, 1917. 

 Scripps Institution for Biological Research, 

 La Jolla, California. 



