C'lIARI.I'.S B. METZ 25 



were unable to confirm certain of these effects. They found very long acrosome 

 filaments on all chiton sperms examined following dilution with sea water. 

 Under similar conditions, 20 per cent of Mytilus sperm had long, fine filaments, 

 whereas the remainder had shorter filaments with a proportionately larger 

 basal acrosome region. These investigators report shorter knob-like acrosomes 

 on living sea urchin (Echinocardium) sperm in contact with glass, but sperm 

 with long filaments as well as others with knob-like acrosomes occurred in 

 formalin-fixed material prepared for electron microscopy. Finally, Rothschild 

 and Tyler found no increase in the proportion of sea urchin {Stronglylocentrotus 

 piirpuratus) sperm with filaments following treatment with egg water. 



It is not immediately apparent why Dan, Colwin and Colwin, and Metz 

 and Morrill on the one hand, and Rothschild and Tyler on the other, fail to 

 agree on three major points, namely /) the relative numbers of sperm with 

 acrosome filaments in sea water suspensions, 2) induction of an acrosome re- 

 action on contact with a surface and j) the effect of egg water. The two groups 

 of investigators even examined the same species, Mytilus eduUs, in one case 

 although it must be admitted that the populations were probably not closely 

 related (Misaki, Japan vs. Millport, Scotland). Point 1 may result from subtle 

 differences in preparation. Wide dilTerences in result might be expected from 

 relatively minor variations in technique if the acrosome reaction is very easily 

 induced by contact with glass. Rothschild and Tyler examined but one species 

 each with regard to points 2 and j. These investigators prepared much of their 

 material for electron microscopy by Anderson's (8) critical point method, which 

 is the method least likely to induce desiccation artifacts. Unfortunately, Dan 

 and Colwin and Colwin give no quantitative data in terms of actual numbers 

 of reacted and unreacted spermatozoa in their experiments. 



In their study, Metz and Morrill (71) examined sperm of Asteriasand Nereis 

 for acrosome filaments. The data are presented in table i. In Asterias, aggluti- 

 nation of sperm by egg water ordinarily occurs only in the presence of an 

 adjuvant (57) and the essential function of this last agent is a metal binding 

 or chelating action (63). Following treatment with sea water or adjuvant 

 (V^ersene) very few Asterias sperms (not over 2 %) were found to have filaments 

 (table i). Spermatozoa of three other asteroids {Luidia clatlirata, Astropecten 

 diiplicatiis, Ilenricia sanguinolenta) also lacked acrosome filaments following 

 sea water or Versene treatment. Likewise, Asterias sperm treated with egg 

 water alone failed to produce filaments in appreciable numbers except in ex- 

 periment 2 (table i). In this experiment the egg water sample was old and 

 agglutinated sperm in the absence of Versene. Treatment with adjuvant and 

 egg water, however, resulted in the appearance of appreciable numbers of 

 sperms with filaments in experiments i, 2 and possibly 4. The role of the adju- 

 vant in this effect is not immediately apparent, for starfish sperm can bind the 

 fertilizin (sperm agglutinin) in egg water, at least in reduced amounts, even 



