ON EGGS OF MARINE ANIMALS 23 



eggs"), free from perivisceral fluid, if from intact ovaries, should 

 be removed as they exude to 250 cc. of sea-water. Sperm thus 

 obtained ("dry sperm") should be kept undiluted and covered 

 until needed for insemination. This is important because the 

 fertilization power of Arhacia sperm-suspensions falls off with 

 dilution (Llllie, 191 5; Cohn, 1917). For insemination a thin 

 sperm-suspension is freshly made. I use one drop of "dry" 

 sperm in 10 cc. of sea-water, from which I take two drops to 

 Inseminate eggs in 250 cc. of sea-water. 



Like those normally shed, these eggs are invariably free from 

 perivisceral fluid and except at the end of the breeding season 

 are of high fertilization capacity. A slight accidental puncture 

 of the ovaries means contamination by the body fluid, which 

 seeps into the ovary and through the genital pores with the 

 extruded eggs. In such an event the eggs must be washed free 

 of the perivisceral fluid which Inhibits fertilization. One should 

 therefore make trial inseminations on samples taken from eggs 

 suspended in 250 cc. of sea-water. If 95 to 100 per cent, of 

 the eggs fertilize as shown by the number that separate normal 

 membranes, they are good. If the per cent, and quality of 

 membrane-separation be low, the worker should wash the eggs 

 again and make another trial insemination on them. This 

 procedure should be repeated during an hour after the eggs 

 have first been suspended In sea-water, until normal fertiliza- 

 tion in close to 100 per cent, of the eggs is obtained. 



The inhibitory action of the perivisceral fluid to the fertiliza- 

 tion of Arhacia eggs was first shown by Lillle. The reader should 

 consult his book, "Problems of Fertilization," for references. 

 I have confirmed LlUie's findings on eggs of Arhacia and on those 

 of Echinarachnius not only for fertilization, but also for experi- 

 mental parthenogenesis. (Just, 1919; 1922.) 



(3) I dare say that the most common method of obtaining 

 Arhacia eggs is that of removing the gonads directly to sea- 

 water. By this method the eggs most certainly suffer from 

 contamination by perivisceral fluid. One may rid them of this 

 as follows: 



Open the animal with a circular cut aborally through the 

 test slightly above the equator. Discard the oral part of the 

 animal. Now invert the aboral part and so drain off and dis- 



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