GERMINAL LOCALIZATION IX THE EGG OF CEREBRATULUS. Ô 



ecto- and entodermal cells and finally turn into pilidia of abnormal 

 sizes and shapes. 



To Professor E. B. Wilson I desire to express my gratitude 

 for kindly suggestions and criticisms. My best thanks are also 

 due to Professor J. S. Kingsley and Dr. Lambert of the 

 Harpswell Laboratory. 



I. Methods and Preparatory Experiments. 



In order to carry out experiments satisfactorily not a little 

 attention was paid to get the water in W'hich embryos were to be 

 reared. It was taken almost every other day in or near mid- 

 stream of the channel in front of the Harpswell Laboratory and 

 filtered throuo;h two sheets of mull or cheese cloth. ' Water taken 

 near the shore contained a considerable quantity of diatoms or 

 other minute suspended particles and was not at all suitable for 

 rearing embryos. 



Pieces of the nemertine, Cerebralulus lacteus, often headless, 

 were kept in glass jars, males and females separate. In this 

 way they lived for some days in excellent condition, but owing 

 to the fact that the longer the specimens were kept in confine- 

 ment the more time was required between fertilization and the 

 first cleavage, those kept over two days were very seldom used 

 in experiments. To obtain eggs one inch or so of a ripe female 

 was cut up in a clean glass vessel with a pair of scissors. By 

 decanting or by removing the eggs with a pipette, eggs free from 

 detritus and ready for experiments w^ere obtained. A very small 

 amount of sperm was extracted by pricking a ripe male with a 

 pipette with a sharp edged mouth and was diluted with fresh 

 sea-water (ca. 40 c.c). To ensure artificial fertilization fresh 

 sperm-water alone was used, though the spermatozoa kept for 



