24 FERTILIZATION 



phoretically homogeneous solution of egg jelly could be absorbed by 

 spermatozoa. In spite of this evidence, Motomura (1950, i953«, b) 

 has claimed that a sperm-agglutinating factor, Cytofertilizin, can 

 be extracted from jelly-free unfertilized eggs of Hemicentrotus 

 pulcherrimus {A. Agassiz) and from the perivitelline fluid of ferti- 

 lized eggs of the same species ; also, that cytofertilizin is secreted, 

 transiently, by fertilized eggs of Strongylocentrotus nudus (A. 

 Agassiz) and Temnopleurus hardwicki (Gray). In the last two cases, 

 the vitelline membrane was removed before fertilization by treat- 

 ment of the unfertilized eggs for 10-15 minutes, with o-5M-NaSCN, 

 so that there was no fertilization membrane and, therefore, no 

 perivitelline fluid at the time when the cytofertilizin was secreted. 

 In spite of being queried by Byers (1951), Motomura's results 

 cannot be ignored or explained away on the basis of species diflfer- 

 ences. The only way of resolving the impasse created by this work 

 is to repeat Motomura's experiments, using his techniques but 

 eggs of Arbacia pimctidata, Arbacia lixula, Paracentrotus lividus, 

 Echinocardium cordatum, Strongylocentrotus purpuratus, or Lyte- 

 chinus pictus (Verrill). Although the agglutination of sea-urchin 

 spermatozoa by homologous egg water is often spontaneously re- 

 versible, this is not always the case. A difficulty therefore arises in 

 distinguishing between irreversible agglutination by homologous 

 fertilizin or cytofertilizin, and irreversible agglutination caused by 

 'unnatural' substances (e.g. cerium ions, Gray, 1920), of which 

 cytofertilizin could conceivably be an example, though this is un- 

 likely. 



The procedure for extracting fertilizin in powder form is given 

 in Table 2 (Tyler, 1949). Defining agglutination titre as the 

 maximum dilution at which agglutination is observed when added 

 to an equal volume of a 1% suspension of spermatozoa (about 

 2.10® sperm /ml.), the egg water from a 20% suspension of eggs, 

 as in Table 2, has an agglutination titre of about 1,000. Fertilizin 

 is a hexosamine-free glycoprotein or mucopolysaccharide contain- 

 ing 20% protein and 80% polysaccharide esterified, according to 

 Vasseur (1952), with one sulphate group per monosaccharide 

 residue; * it is highly acidic, the electrophoretic mobility, about 

 18 X io~^ cm-/sec./volt, towards the anode, changing little as the 

 pH is lowered from 8-6 to 2-0 (Runnstrom et al., 1942; Tyler, 



* The amounts of sulphate found in the molecule are not always consistent 

 with this arrangement. 



