52 BASIC METHODS FOR EXPERIMENTS 



On the basis of my experience with the eggs of these two 

 forms and with several species of echinids in European waters, 

 I suggest as general rule of procedure the following: 



(i) Take always unfertilized eggs known by previous trial 

 inseminations of samples of them to be in optimum fertilizable 

 condition. (2) Expose them to 2 cc. N }4o normal butyric 

 acid added to 50 cc. of sea-water and thoroughly dissolved by 

 vigorous shaking. (3) At ten second intervals remove i cc. 

 of the eggs to 250 cc. of sea-water, establishing thus a series of 

 10 to 12 numbers in order to determine that exposure which 

 gives the highest per cent, of membrane-separation. (4) Expose 

 to the butyric acid sea-water another lot of eggs from the same 

 female for that length of time found to be the optimum, removing 

 the eggs all to 1000 cc. of sea-water. (5) Remove at intervals of 

 five minutes 4 lots of the eggs from sea-water each to 50 cc. 

 of sea-water plus 8 cc. of 2.5M NaCl. (6) At intervals of five 

 minutes during twenty-five minutes remove samples of the eggs 

 from the hypertonic sea-water to 1000 cc. of normal sea-water. 

 By (5) and (6) one establishes (a) the optimum residence of the 

 eggs in sea-water and (b) their optimum exposure to hypertonic 

 sea-water for the production of top-swimming plutei. 



Literature 



Clowes, G. H. A. and Smith, H. W. 1923. The influence of 

 hydrogen ion concentration on the fertilization and growth of 

 certain marine eggs. Amer. Journ. Physiol., Vol. 64. 



Delage, Y. 1902^. L'acide carbonique comme agent de choix de 

 la parthenogenese experimentale. C. R. Acad. Sci. CXXXV. 



. igoib. Sur le mode d'action de l'acide carbonique dans la 



parthenogenese experimentale. C. R. Acad. Sci. CXXXV. 



. I902f. Nouvelles recherches sur la parthenogenese experi- 

 mentale chez Asterias glacialis. Arch. Zool. Exp. Ser.3. X. 



. 1910. La parthenogenese experimentale. Verh. VIIL In- 



ternat. Zool. Kongress., Graz. 



Heilbrunn, L. V. 1915. Studies in artificial parthenogenesis. IL 



Physical changes in the egg of Arbacia. Biol. Bull., Vol. 29. 

 Just, E. E. 191 5. Initiation of development in Nereis. Biol. Bull., 



Vol. 28. 

 . 1919- The fertilization reaction in Echinarachnius parma. 



in. The nature of the activation of the egg by butyric acid. 



Biol. Bull., Vol. 36. 



