46 E. E. JUST. 



develop into plutei that swim to the top of the dishes. Mixtures 

 in the proportions 5, 6, 7 and 8 c.c. of 2.5 M NaCl plus 50 c.c. 

 of sea-water in each case were employed. The best results were 

 obtained with the mixture of salt and sea-water in the proportions 

 of 5 cc.. of 2.5 M. NaCl plus 50 c.c. of sea-water. 1 The procedure 

 was as follows: Eggs exposed to butyric acid sea-water were 

 removed at intervals of 5 seconds to 250 c.c. of sea-water. Fol- 

 lowing about 20 minutes in sea-water eggs were carried over to 

 dishes of hypertonic sea-water at 15, 20, 25, etc., minutes. 

 Twenty-five minutes treatment is best. Eggs previously exposed 

 to butyric acid for 35 seconds (optimum exposure for membranes) 

 gave the highest per cent, of cleavage and the best type of development. 

 It would be tedious to cite individual experiments on this 

 point. The reader would scarcely be interested in experimental 

 details on the rather threadbare subject of the effect of hypertonic 

 sea-water following butyric activation. It is, of course, generally 

 understood that hypertonic sea-water is most successful sub- 

 sequent to butyric acid treatment where membranes have been 

 formed. There would certainly be no reason to use butyric acid 

 if this were not true. Notwithstanding all this, I wish to em- 

 phasize that those eggs with the highest per cent, membranes 

 (optimum exposure) yield best to hypertonic treatment. Eggs 

 under- or over-exposed to butyric acid do not give the same type 

 of development. 2 



B. Effect of Insemination Following Butyric Acid Activation. 



After removal to normal sea-water following optimum exposure 

 to butyric acid sea-water Echinarachnius eggs form 100 per cent. 



1 The 2.5 M. NaCl solution was always freshly made. No solution was ever 

 older than six hours when added to the sea-water. 



- The successfully treated eggs are certainly very beautiful; as far as the gastrula 

 stage in most cases they appear to be perfectly normal. The plutei develop more 

 slowly than those from fertilized eggs and are not so hardy. Possibly, with even 

 nicer treatment, the development could be improved. 



Cytological study of eggs induced to develop with artificial means has been made 

 by Wilson, Hindle and Herlant. In the living Echinarachnius egg we observe that 

 while in sea-water following butyric acid treatment a monaster forms beyond 

 which stage the egg does not develop. Having been properly exposed to hyper- 

 tonic sea-water the egg forms in sea-water a complete astral system. Overex- 

 posure to hypertonic sea-water results in the formation of innumerable asters when 

 the egg is removed to sea-water: such eggs fail to cleave or form very irregular 

 cleavages. 



