2O6 MYRA M. SAMPSON 7 . 



CONCLUSIONS. 



Ova of S. franciscanus exposed to sperm filtrates, concentrated 

 sperm suspensions, or to blood serum of Katharina tunicata for 

 one to three minutes formed typical fertilization membranes. 

 Subsequent treatment with Loeb's hypertonic sea-water for 

 seventy minutes caused a large percentage of those with mem- 

 branes to develop into gastrulae and plutei. Every precaution 

 was taken to avoid contamination of the sperm suspensions 

 of the chiton with body fluids or serum. It seems probable 

 that the membrane formation in the filtrates and in the con- 

 centrated sperm suspensions is formed by some substance 

 derived from the sperm. 1 The nature of this substance has not 

 been determined. Experiments with filtrates of sperm of 

 Arbacia, S. purpuratus and 5. franciscanns and Nereis indicate 

 that it is an organic compound (Sampson, 1926). The effect 

 produced by the serum is probably due to organic compounds 

 present in the latter. 



Similar results were obtained with ova of S. franciscanus 

 which were treated with concentrated sperm suspensions and 

 with dilute serum of two other chitons, Ishnochiton magdalensis 

 and Cryptochiton. With ova of 6 1 . purpuratus no typical mem- 

 branes formed in the preparations used, and the fertilization 

 capacity of the treated eggs appeared to be normal. 



LITERATURE. 

 Elder, J. C. 



'n Archiv. f. Entw.-mech., 35, 145-163. 

 Heath, Harold. 



'99 Zool. Jahrbuch., 12, 567-657. 

 Kupelwieser, Hans. 



'06 Biol. Centralbl., 26, 744-748. 



'09 Archiv. f. Entw.-mech., 27, 434-462. 

 Loeb, J. 



'oya Pfluger's Archiv., 118, 36-41. 



'076 Univ. of Calif. Pub. Physiol., 3, 57-58. 



'o8a Pfluger's Archiv., 122, 196. 



'o8/; Pfluger's Archiv., 124, 37. 



'15 Amer. Nat., 49, 257-285. 

 Sampson, Lillian. 



'95 Jour. Morph., u, 596-628. 

 Sampson, Myra M. 



'26 Biol. Bull., 50, April, 1926. 

 Robertson, T. B. 



'12 Archiv. f. Entw.-mech., 35, 64-130. 



1 A membrane swelling has been observed in concentrated suspensions of sperm 

 by Heilbrunn (BiOL. BI/LL., 29, p. 149-203), and attributed by him to a substance 

 produced by sperm. 



