214 NEIL S. DUNGAY. 



They also throw light upon the theories dealing with the produc- 

 tion of defectives by the action of injurious agencies upon the 

 germ cells previous to the time of fertilization. 



The experimental work was done at the Marine Biological 

 Laboratory at Woods Hole, Mass., during the summers of 1911 

 and 1912. The results given are based upon observations made 

 upon more than 600 cultures of living Nereis eggs and 200 cul- 

 tures of Arbacia eggs. Samples from the various cultures were 

 preserved for later cytological study, the results of which are 

 also reported in this paper. 



II. MATERIALS AND GENERAL METHODS. 



A. Occurrence. 



In the evening from the time of darkening until about ten 

 o'clock, sexually mature males and females of Nereis limbata 

 swim freely at the surface of the Eel Pond at Woods Hole. 

 Although they are most easily collected during the two weeks 

 following the full moon, it is possible to find a few nearly every 

 evening of the lunar month. The breeding habits have recently 

 been described (Lillie and Just, '13) in a very interesting paper 

 which gives in considerable detail the methods of catching and 

 keeping the worms. 



B. Collecting. 



For my experiments the animals were caught in nets by 

 lantern light, placed in separate finger bowls of sea water, and 

 taken to the laboratory buildings at about 9:30 P.M. The 

 worms were then washed in running sea water and the finger 

 bowls were cleansed and refilled, covered with glass plates and 

 placed in running water to keep cool. Early the next morning 

 the accumulations of mucus were removed and the water was 

 again changed. When carefully cared for in this manner, very 

 few of the worms shed their germ cells during the night. The 

 males practically never shed their sperm cells under these condi- 

 tions. During one month in which a record was kept, over 90 

 per cent, of the females captured retained their eggs. By this 

 method I have sometimes kept the females without shedding for 

 as long as 60 hours, though, for experimental purposes, the eggs 



