844 



SCIENCE 



[N. S. Vol. XXXVII. No. 961 



dition for the formation of the fertilization 

 membrane in many animal eggs is an increased 

 permeability of the plasma membrane for sub- 

 stances which pass out and harden in con- 

 tact with the sea-water. The role of the acid, 

 etc., in membrane formation is held by many 

 to be the increasing of the permeability of the 

 plasma membrane of the egg. 



That the first effect of the sperm of the 

 FucacesB upon the egg is to cause cell-wall 

 formation, conditioned as it seems to me by a 

 momentarily increased permeability of the 

 plasma membrane just as in certain animal 

 eggs, is apparent from the observations of sev- 

 eral investigators. Farmer and Williams fur- 

 nish remarkable evidence showing that the en- 

 trance of the sperm supplies the stimulus 

 which leads to the formation of the cell-wall 

 in Halidrys. In this form pieces of the 

 oospheres are sometimes pinched off during 

 extrusion. These observers note that such 

 pieces sometimes attract the sperms and be- 

 come fertilized, surrounding themselves with 

 a cell-wall in the normal way. The cases of 

 merogony induced by Winkler in Cystosira 

 barbata may, I think, be explained by as- 

 suming that the sperms increase the permea- 

 bility of the non-nucleated fragments, as well 

 as being the underlying cause of further de- 

 velopment. In the normally fertilized eggs of 

 Halidrys Farmer and Williams note that the 

 entrance of the sperm causes the eggs to swell 

 and become more transparent. In some cases 

 movements of vacuoles are discernible and the 

 nucleus may change its position. They con- 

 clude that these alterations ensue as a defi- 

 nite result of the stimulus given by the sperm. 

 The fertilized egg becomes covered by conical 

 projections, from each of which a fine thread 

 projects, consisting of a series of droplets. 

 After 3-5 minutes the fertilized egg resumes 

 its spherical shape and decreases in diameter. 

 They also observed that the sperms were re- 

 pelled from fertilized eggs and conclude that 

 this is due to the excretion of some substance 

 which exerts a negative chemotaetic and in- 

 jurious effect on the sperms. Such eggs at 

 once become invested in cell-walls, while 



others not exliibiting these phenomena after a 

 time degenerate. 



The results of my experiments, in which 

 cell-wall formation and subsequent develop- 

 ment were induced in unfertilized eggs of 

 Fucus, and the data mentioned above, seem 

 to show that the first effect produced by the 

 sperm upon the egg is purely superficial, caus- 

 ing an increase in the permeability of the 

 plasma membrane. These conclusions are in 

 harmony with those of certain animal physiol- 

 ogists. Therefore, theoretical considerations 

 as to the causes of the change in permeability 

 and the stimulus to further development need 

 not be discussed here. 



As yet I have been unable to investigate the 

 nuclear behavior of the parthenogenetic plants 

 of Fucus. Farmer and Williams, agreeing 

 with Strasburger, hold that the Fucus plant 

 contains the diploid number of chromosomes 

 and that the reduction to the haploid number 

 occurs during the first division in the oogone 

 and in the antherid. Since the eggs of these 

 plants induced to develop without fertilization 

 contain the haploid number of chromosomes, 

 one can assume, unless a regenerative doub- 

 ling in their chromosome number occurs, that 

 the nuclei of the sporelings contain the hap- 

 loid number. It would be of interest to grow 

 these parthenogenetic sporelings to sexual ma- 

 turity and to investigate the chromosome be- 

 havior especially during oogenesis and sperma- 

 togenesis. Hoyt has carried sporelings of 

 Diciyota to maturity by sowing the spores on 

 oyster shells, and transferring these to the 

 open water after the sporelings had become 

 firmly attached. Lewis had used similar 

 methods successfully with the sporelings of 

 certain Florideae. Fertilized eggs of Fucus 

 when allowed to settle down on oyster shells in 

 the bottom of dishes become firmly attached 

 and produce the sporelings. Fucus eggs in- 

 duced to develop by artificial stimuli also pro- 

 duce sporelings on oyster shells. For lack of 

 time I was unable to transfer them to the 

 open water, but the method is suggestive. 



J. B. Overton 

 Ukiveesitt of Wisconsin 



