C. B. METZ 29 



The situation with respect to increase in respiration appears to 

 be somewhat more compHcated. In some forms metal binding 

 agents fail to increase the oxygen uptake but do increase anaero- 

 bic metabolism of sperm (e.g., Lytechinus pictus, Tyler and 

 Rothschild, 1951 ) . In the starfish, however, similar agents clearly 

 increase oxygen uptake of sperm (e.g., Asterias forbesii, Metz 

 and Birky, 1955). Irrespective of whether the agents increase 

 aerobic or anaerobic energy yielding systems, egg water and 

 metal binding agents should have similar action on sperm respira- 

 tion if their mechanisms of action are the same. In some forms 

 such parallel action has been reported, but in others conflicting 

 data prevent a clear decision. It is evident from the available data 

 (Table I) that the problem requires further investigation. 



Effect of Egg Water on Sperm Morphology. Studies (re- 

 viewed by Colwin and Colwin, this volume, Dan, 1956, and Metz, 

 1956) have shown that the sperm acrosome of a variety of forms 

 (24 species in 4 phyla) undergoes a striking change under cer- 

 tain conditions. The change, known as the acrosome reaction, in- 

 volves the conversion of the normally compact acrosome into a 

 filament. 



This discovery has contributed substantially to our understand- 

 ing of the morphology of fertilization. Specifically it has provided 

 a satisfactory explanation for the filaments that extend between 

 the egg surface and the sperm in the early stages of fertilization 

 of some forms (see Colwin and Colwin, this volume; Dan, 1954a, 

 1956). 



The acrosome reaction has been reported to result under a 

 variety of conditions. These include contact of the sperm with a 

 surface such as glass or the egg, exposure to alkaline sea water, 

 or low temperature and treatment with excess calcium or egg 

 water (Dan, 1952, 1954a,b; Dan and Wada, 1955; Wada, Collier, 

 and Dan, 1956; A. L. Colwin and L. H. Colwin, 1955; L. H. Col- 

 win and A. L. Colwin, 1955a,b; Metz and Morrill, 1955). In 

 fact the reaction sometimes occurs in a high proportion of sperm 

 after dilution with sea water (Rothschild and Tyler, 1955). Of 

 these conditions the treatment with egg water is of special in- 

 terest, for it suggests the possibility that the acrosome reaction 



