402 TREADWELL. [Vol. XVII. 



arising from an excessive number of sperm collected on the 

 surface of the Q^'g can be avoided. 



While emitting the sexual products, the female usually 

 crawls slowly along the bottom of the dish, the eggs stream- 

 ing out from both sides of the body through openings at the 

 base of the parapodia. Occasionally one will be found swim- 

 ming with considerable rapidity during this process. The 

 males are usually much more active at this time, though there 

 is never anything like the amount of activity displayed by some 

 other free-swimming annelids, e.g., Nereis. 



Material obtained and fertilized in this way was preserved 

 at intervals of fifteen minutes for the first twelve hours, and 

 at rather longer intervals for the later stages. There is so 

 much variation in rate of development in the different lots, 

 due apparently to temperature conditions, that time records 

 are of little value, and I have not attempted to keep them 

 after the first few divisions. 



For preserving, I have found Kleinenberg's picro sulphuric 

 (dilute) and picro acetic (made with i % acetic) the most 

 useful, the latter especially, when followed by Delafield's 

 haematoxylin ^ (acidified), giving beautiful results with surface 

 views. Flemming's fluid, though practically worthless for sur- 

 face views, preserves cilia well, and gives better preserva- 

 tion for sectioning than the picro acetic. The specimens, 

 preserved and stained as above, were cleared in clove oil and 

 mounted in the same medium underneath a long cover-glass, 

 supported at one end by a bit of capillary glass tubing. This 

 method, for which I am indebted to my friend Dr. C. M. Child, 

 has proved much more satisfactory than to mount in balsam, 

 as the specimens can be rolled into any desired position and 

 drawn with a camera as soon as they are mounted. 



In the main I have followed Mead's nomenclature (No. 22) 

 with certain modifications suggested in conference with Dr. 

 Child, whose work on Arenicola has been carried on at the 

 same time as this. The successive generations of " macro- 

 meres " we propose to designate by capital letters, with the 



1 I am under great obligations to Dr. Conklin for suggestions as to the use of 

 this method. 



