322 MYRA MELISSA SAMPSON. 



the Nereis were collected. In this experiment the majority of 

 the eggs matured. The maturation was almost as rapid as in 

 fertilized eggs but the subsequent segmentation and development 

 was slow and abnormal. Segmentation into two, four, and 

 eight cells was observed and verified for me by Dr. Alvalyn 

 Woodward. Free swimming trochophores developed which were 

 abnormal in shape, internal structure, and in the distribution of 

 cilia. In no case did such changes occur in the sea-water 

 controls. Similar results were obtained with four sperm filtrates 

 of Nereis limbata. 



Summary of the Effects of Sperm Filtrates and Dialyzates on 

 Ova of the Same Species. Sperm filtrates and dialyzates of 

 Arbacia punctulata, and sperm filtrates of Strongylocentrotus 

 purpuratus, of Strongylocentrotus franciscanus, and of Nereis 

 limbata produce marked changes in ova of the same species. 

 These are characterized by changes in form; nuclear and cell 

 division ; and, with the exception of Nereis limbata, by subsequent 

 fragmentation and cytolysis. "Fragmentation" is a separation 

 of the segments due possibly to a lack of a fertilization membrane. 

 In Nereis limbata the sperm filtrates cause maturation ; formation 

 of fertilization membranes; segmentation; and, in a low per- 

 centage of cases, the development of abnormal larvae. 



V. FILTRATES AS FACTORS IN PARTHENOGENESIS. 



It seemed possible in view of the results obtained by Loeb 

 (1905) and others that the ova of sea-urchins, treated with 

 filtrates of sperm, might develop perfectly if they were subse- 

 quently exposed for a brief period to Loeb's "hypertonic sea- 

 water". In Loeb's experiments, exposure of unfertilized ova of 

 sea-urchins to hypertonic sea-water, at the temperature pre- 

 vailing during the breeding season, produced development in a 

 very small percentage of the ova. Fertilization membranes did 

 not form usually and the developing plutei did not swim at the 

 surface of the water as did normal plutei. A brief preliminary 

 treatment of the ova with a very dilute solution of butyric acid 

 increased the percentage of ova which developed, and the latter 

 were normal in macroscopic structure and in their reactions. 

 Recently Just (1922), employing a greater concentration than 



