2l8 NEIL S. DUNGAY. 



they will tend to be taken from the cultures in greater proportions 

 in the earlier part of the preserved series. An effort was made 

 to overcome this by using several parallel cultures in different 

 dishes but without entire success since the number of eggs from 

 a single female is limited and since it does not seem wise to use 

 eggs from two or more females, in the same experiment. 



III. OUTLINE OF DEVELOPMENT OF NEREIS EGGS. 



Although the maturation, fertilization, and development of 

 the egg of Nereis have been described in more or less detail by 

 others (e. g., Wilson, '92, Lillie, F. R., 'n, and '12) it seems desir- 

 able to review' a few of the principal points at this time. The 

 eggs, which vary considerably in size, are about 100 microns in 

 diameter. Their irregular shape at the time of laying is soon 

 lost and they take the form of a sphere slightly compressed in a 

 polar direction. They are of a greenish color and moderately 

 transparent. A polar view, which is the one usually obtained, 

 shows the large germinal vesicle in the center of the egg and an 

 imperfect double belt of la'rge oil drops, numbering approxi- 

 mately from ten to twenty. Just beneath the vitelline membrane 

 is a radially striated cortical layer which breaks down imme- 

 diately following insemination, throwing off a thick envelope of 

 jelly and leaving a conspicuous perivitelline space. The jelly is 

 readily demonstrated by the use of India ink ground up in sea 

 water, although it is nearly invisible in pure sea water. Since 

 the unfertilized eggs normally lie in contact at the bottom of a 

 dish and, upon insemination, become separated by the jelly, it 

 is easy for the naked eye to determine whether or not a large 

 part of the eggs have started to develop. A microscope, how- 

 ever, is necessary to determine the condition of any individual 

 egg. As a general rule unfertilized eggs do not form jelly upon 

 standing undisturbed, at least not for several hours. Yet close 

 examination usually reveals a mere trace of eggs which have 

 formed this secretion. Inasmuch as strong mechanical agitation 

 will induce jelly formation this is perhaps due to violent contact 

 with the scissors upon opening the female, or possibly there may 

 be a few eggs which are extraordinarily sensitive to stimulation. 

 The latter view is rendered probable by the fact that the pro- 



