304 MVRA MELISSA SAMPSON. 



placed on opposite sides of the operator. Each animal, unless 

 shedding freely, is immediately wiped and placed on its aboral 

 surface in a Syracuse watch glass. In this position the repro- 

 ductive cells exude through the genital pores. In a second 

 method suggested by Dr. Glaser, the spines are rubbed off before 

 the animals are washed and dried. If the reproductive elements 

 are ripe, shedding begins immediately and it is unnecessary to 

 cut the "test." There is no admixture with body fluids or 

 with sea-water and very clean dry reproductive cells are obtained. 

 Only ripe spermatozoa are shed and these are collected in a 

 beaker. Not all the eggs shed are ripe. For this reason it is 

 necessary to fertilize a sample of eggs from each female. After 

 this the "certified" eggs are placed together in a finger bowl 

 with sufficient sea-water to keep the concentration of egg-water 

 below a point at which it will injure the eggs. 



Method of Obtaining Ripe Eggs of Nereis limbata. The method 

 recommended by Lillie (1911) and Just (19150) was employed. 

 Males and females as they were caught were segregated in finger 

 bowls of sea-water and kept cool until all preparations for an 

 experiment were complete. The most satisfactory results are 

 usually obtained with reproductive cells taken from such animals 

 within two hours after collection ; although, if necessary, shedding 

 can be prevented for twelve hours or more if the dishes containing 

 the animals are kept on ice. Since either drying the animals on 

 filter paper or washing them in distilled water leads to shedding, 

 each animal was "sterilized" by first transferring it to a finger 

 bowl containing two hundred and fifty milliliters of sea-water. 

 (In this volume of sea-water any sperm adhering to the body of 

 the female will lose their fertilizing power.) Subsequently each 

 animal was placed in a dry Syracuse watch glass in which any 

 excess of moisture was absorbed with strips of filter paper, and 

 there cut transversely with sterilized scissors. The eggs or 

 sperm were forced out by the spasmodic contractions of the 

 body muscles. To avoid accidental insemination the males were 

 opened with a second set of instruments; and all inseminated 

 controls were kept separate from the experiments in which 

 special solutions were being tested. Eggs and sperm were kept 

 covered and cool until used. 



