PARTHENOGENESIS IN THE SEA URCHIN. 2O3 



which were used in these experiments. All of these occur in 

 similar situations within Monterey Bay. Where easy of access 

 they are not as abundant, because they serve as food for the 

 Japanese and the Italians of the region. S. franciscanus is to 

 be found from a few to many feet below low water line and 5. 

 purpuralus just below this line. On calm days both species can 

 be seen at depths of twenty teet and hundreds of feet from shore. 

 5. franciscanus is rarely exposed at the lowest tides, whereas S. 

 purpuratus is commonly found in isolated tide pools or completely 

 exposed at low tide. In many locations this species is so 

 abundant that the rocks are carpeted with this purple sea-urchin. 

 The chitons adhere to the rocks by their pedal muscles (Samp- 

 son, 1894), an d are exposed only at the lowest tides. 



Ripe gametes of 5. purpuratus were available from December 

 until June and continued to be so, according to Dr. Fisher, 

 until the middle of July in individuals from certain locations. 

 In sheltered parts of Monterey Bay all individuals shed during 

 the week of March 26, following a series of heavy rains. During 

 the first week of May a similar shedding occurred at "Parke 

 Davis Point," a sheltered location on the Pacific coast. In the 

 most exposed collecting area, shedding had not occurred before 

 the middle of July. Elder (1911) and Loeb (1915) have recorded 

 similar breeding habits for this species. Few individuals of S. 

 franciscanus contained fully developed gonads before April. The 

 unusually cold season probably accounts for their slow de- 

 velopment, as Dr. Frank Lillie had obtained plenty of ripe indi- 

 viduals in January and February of the preceding year in similar 

 locations. In the chitons ripe spermatozoa were present in March, 

 but ripe eggs were not obtained until the first week in May. In 

 K. tunicata, according to a personal communication from Dr. 

 Gertrude Van Wagenen, eggs were not shed until late in July in 

 exposed locations. Heath (1899) states that the eggs of Ishno- 

 chiton are shed in May and June. 



METHODS. 



In the sea-urchins the oral disc was cut away; the contents of 

 the body cavity, with the exception of the gonads, removed; 

 and the body cavity thoroughly irrigated with filtered sea-water. 1 



1 All sea-water was obtained directly from Monterey Bay and filtered. Because 



