2 MARGARET MORRIS 



developed to larvae. There might, of course, be some other 

 way in which eggs without polar bodies could develop, and those 

 in which the fusion of nuclei took place might prove to be, . 

 after all, incapable of further development. Finally, besides 

 settling this question, it was thought that a study of the pre- 

 served material would throw Ught on the question as to which 

 of the two maturation divisions was the true reducing division. 



II. METHODS 



a. Experimental. Cumingia is fairly common in the waters 

 around Woods Hole, and each female, when ripe, yields a large 

 number of eggs. The animals are brought in dry, and do not 

 begin to spawn until placed in sea-water. It is therefore easy 

 to obtain eggs free from contamination by sperm, by placing 

 each individual in a separate dish of water. To guard further 

 against contamination by sperm the usual precautions with 

 regard to clean dishes were observed. Controls of all the ex- 

 periments were kept and carefully watched. Very little tend- 

 ency towards parthenogenetic development such as Morgan 

 ('10) observed in the course of his experiments on Cumingia was 

 seen in these controls. In one case a few eggs were found which 

 had formed the first polar body, but no cleavage stages or 

 larvae were found in this or in any other control. 



The agents used to obtain parthenogenetic development in 

 these experiments were heat and hypertonic sea-water. Heat 

 alone, hypertonic sea-water alone, and hypertonic sea-water fol- 

 lowed by heat gave some development, but the results were 

 not so satisfactory as when heat was used first and followed by 

 hypertonic sea-water. This is, of course, in accord with Loeb's 

 method of artificial parthenogenesis, in which a cytolytic agent 

 is followed by a 'corrective.' It does not come within the scope 

 of the present study to say whether the effect of the hypertonic 

 sea-water is in fact corrective as Loeb thinks, or additive as R. 

 S. Lillie has maintained more recently. Loeb and Wasteneys 

 induced normal segmentation and formation of larvae in the 

 eggs of Cumingia by sensitizing them with SrCl2 and treating 



