2O4 MVKA M. SAMPSON. 



The gonads were transferred to Syracuse watch glasses, in which 

 they shed their reproductive cells. 1 The gonads ot the chitons 

 lie just beneath the dorsal shells, and were exposed either by 

 removing the latter or by removing the muscles and the viscera 

 ventral to the gonads. The body cavity was thoroughly washed 

 with filtered sea-water and the gonads placed in Syracuse watch 

 glasses. The body fluid was obtained by piercing the pedal 

 muscles of the chitons and allowing the body fluids to drain out 

 into finger bowls. These fluids were then filtered through double 

 layers of filter paper. 



The filtrate of sperm suspension of K. tunicata was prepared 

 by filtering ten per cent, sperm suspensions of this species through 

 tested Mandler filters according to the method used in another 

 investigation (Sampson, 1926). 



RESULTS. 



Exposure of the ova of 5. franciscanus to a filtrate of a ten 

 per cent, sperm suspension of Katharina tunicata for one to 

 twenty minutes led to the formation of perfect fertilization 

 membranes in the majority of the ova. If transferred to sea- 

 water cytolysis occurred very rapidly in those eggs possessing 

 membranes. If exposed for sixty to eighty minutes to hypertonic 

 sea water many of those with membranes developed into gastrulae 

 and plutei which were normal in appearance. 2 



In highly concentrated sperm suspensions of K. tunicata the 

 ova of S. franciscanus formed membranes within one to three 

 minutes. From forty to sixty per cent, of the ova were so 

 affected. Within ten minutes these membranes were perfect in 

 contour. Dilute suspensions of spermatozoa were ineffective. 

 The spermatozoa of this species are inactive in sea-water and in 



of copper in the pipes the running sea-water in the laboratory could not be used, 

 nor could water be carried in galvanized iron pails. Enough zinc dissolved in the 

 sea-water in transit to prevent the fertilization of eggs in it, or to prevent the 

 fertilization of ova from females washed in such water. 



1 This proved to be the most satisfactory method of obtaining the reproductive 

 cells from 5. franciscanus, partly because of the large size of this sea-urchin and 

 partly because the reproductive cells were so concentrated and so viscous that 

 they did not shed readily through the genital pores. 



2 Ova of Nereis exposed to the sperm filtrate only of Arbacia formed membranes, 

 maturated, and a small percentage of those with nu inbi.inc s segmented normally 

 and developed into abnormal trochophorfs (Sampson, 1926). 



