FERTILIZATION IN PLATYNEREIS MEGALOPS. 1 01 



August 8, 1912, 2 P.M., six hours after laying of 10,851 eggs 

 (from one female) six per cent, were still in the germinal vesicle 

 stage. Other counts of living eggs and of sections show higher 

 percentages. Every egg laid the night of capture cleaves. Dry 

 inseminations, day or night, at best never give more than ninety 

 per cent, of cleavages. The poor quality of the animals after 

 several hours in the laboratory may account for the failure of the 

 dry eggs X washed sperm A.M. group to cleave. But since the 

 dry eggs X dry sperm A.M. series gives cleavage, I am rather 

 inclined to believe that the method used was poor: for instance, 

 the filter paper then used was too soft allowing the loss of most of 

 the spermatozoa or too much water was left when the dry eggs 

 were added. 



The results with dry eggs X washed sperm, P.M. group are 

 wonderfully uniform and show conclusively that the sea-water, 

 at least for the exposures used, has no harmful effect on the sperm. 

 The method used is simple. As soon as possible after capture one 

 to three males are cut up in from 8 drops to 20 c.c. of sea-water 

 and allowed to stand upward to twenty minutes. (The sperm 

 are active after having been in sea-water for twelve hours.) The 

 sperm suspension is then filtered. I used a very hard filter 

 paper. This paper was then tilted and thoroughly drained 

 until under the lamplight the glistening water was thoroughly 

 absorbed. A dried female was cut up on the filter paper or 

 pricked and the eggs thus procured rolled over the paper to reach 

 the sperm left behind or caught in the pores of the filter. The 

 whole was then put in a dish of clean sea-water. It would be 

 tedious to cite the individual experiments. They show conclus- 

 ively that dry eggs inseminated with washed sperm develop in 

 normal fashion. 



Now since, as has been shown above, there is a minimal 

 amount of sea- water that will permit fertilization, dry eggs 

 ought to fertilize if put on the filter paper before all the water 

 has been absorbed. Such indeed is the case. Moreover, dry 

 eggs put in two drops of thin sperm suspension develop. From 

 a suspension made by cutting up one or more males in sea-water 

 two drops are taken. Dry eggs put in this cleave and next 

 morning swim. 



