No. 3.] PODARKE OBSCURA VERRILL. 40 1 



Artificial fertilization, though tried repeatedly and at various 

 times of the day, was never successful, unless the eggs had 

 been laid in the normal manner by the female. Then it was 

 perfectly possible to cut sperm from the body of the male and 

 fertilize. Since, as already stated, the normal time of laying 

 is from 7.30 to 9 p.m., many important early stages are 

 passed through before daylight (the embryo begins to swim 

 at the completion of the 64-cell stage, or about the fifth hour 

 of development), and since the small size and opacity of the 

 embryo make it an unfavorable object for study by artificial 

 light, an attempt was made to delay the process of laying. 

 Although a number of devices which had proved successful in 

 other forms were tried, they were wholly without success. If 

 the females are put on ice, or in a very cool place, overnight, 

 they will hold their eggs until about daylight the next morn- 

 ing, but such eggs almost invariably developed abnormally ; 

 and the same result followed if for any reason the eggs were 

 laid at other than the regular time. In one case only did I find 

 eggs which must have been laid about 4 a.m. developing nor- 

 mally. It is not at all improbable that modifications of the 

 cooling method might have proved successful, but for the pur- 

 poses of this paper preserved material was so much more satis- 

 factory than fresh that I have relied almost entirely on that, 

 merely using the fresh, where possible, for corroboration. 

 Cilia can of course be seen better in living than in preserved 

 material, but the history of cells can best be made out on 

 stained specimens where the karyokinetic figures give abso- 

 lutely accurate evidence of cell origin. 



When the sexual products are ripe, the sexes may be easily 

 distinguished by the characteristic color of the ova and sperm 

 seen through the semi-transparent body wall ; the females 

 being a seal brown, the males a cream color. I found that 

 the most convenient way was to isolate the sexes, which 

 seems in no way to affect the time of egg-laying, and when 

 laid to transfer the eggs to fresh water and fertilize with sperm 

 cut from the body of the male. In this way the precise time 

 of fertilization can be controlled, something which cannot 

 always be done if the sexes are together ; and the difficulties 



