32 



PHYSIOLOGICAL TRIGGERS 



The suboptimal fertilization of underripe and overripe eggs can be substan- 

 tially corrected by fertilization of the eggs in solutions of proteins, amino 

 acids or Versene (ii, 34, 103). These agents presumably act by binding metals 

 which have an inhibitory action on fertilization. 



An analysis of the mechanism of action in this fertilization improving effect 

 might properly begin with the question whether the chelating agent acts upon 

 the sperm, the egg or both gametes. The chelating agents clearly affect unferti- 

 lized eggs. The effects include a swelling of the jelly, a rounding of eggs, an 

 increased stretching in the centrifugal field (11, 46, 99), and an increase in the 

 rate of smoothing of the wrinkles produced by hypertonic sea water treatment 

 (132). Runnstrom and his colleagues appear to regard the fertilization-improving 

 action of chelating agents as mainly an action on the eggs. However, before 

 accepting this view, a more direct study of the problem would appear to be 

 in order. 



The writer puts a somewhat different interpretation on conditions observed 

 in Arbacia punchdata from Florida waters. The animals in the local population 

 definitely contain gametes from September until June. They have not been 

 examined thoroughly during the summer months. From late January until 

 October (with the possible exception of the summer) the Arbacia yield quanti- 

 ties of gametes. The eggs fertilize readily in sea water, form good fertilization 

 membranes and cleave normally. However, beginning in October or November 

 and continuing through December the animals yield decreasing amounts of 

 gametes, and these become progressively more difficult to fertilize. The eggs 

 that do fertilize are frequently polyspermic and fail to elevate normal mem- 

 branes. A few tests have shown that these 'winter eggs' fertilize normally in 

 Versene-sea water. Although no serious study of this annual cycle in the Florida 

 Arbacia has yet been made, the writer hazards the view that the animals 

 actively produce gametes from February until September or October at which 

 time gametogenesis ceases. The gametes remaining in the gonads beyond this 

 date are neither resorbed nor spawned. These 'stored' gametes become pro- 

 gressively less fertilizable. In view of the correcting effect of Versene on these 

 'stored' gametes it appears likely that the storage is associated with an accumu- 

 lation of metals which inhibit fertilization. It will be interesting in this case 

 also to determine whether the action of Versene is upon the sperm, the egg or 

 both gametes. 



A thorough examination of both the Swedish and Florida material in this 

 regard seems especially desirable in view of the findings of Tyler and x'Vtkinson 

 (120) and Tyler (118). These investigators find that Lytechinus eggs form 

 poor fertilization membranes when inseminated with aged sperm (see also 

 ref. 98). This effect is corrected by treatment of the sperm alone with \'ersene 

 or other chelating agents. On the other hand, no improvement results when 

 eggs alone are treated with \>rsene, washed in sea water and inseminated in 



