Sabellariidae 189 



rounded egg is fifty-six micra; the membrane, usually wrinkled, is about 

 twelve micra from the egg surface. Fine protoplasmic processes are 

 seen to extend from the egg surface as the membrane is raised. The 

 elevation of the membrane is apparently due to the swelling of a rather 

 dense jelly situated between the egg surface and the membrane. This 

 jelly is ordinarily invisible but it can be demonstrated by removing the 

 outer membrane (see p. 190) and placing the eggs in a dense suspension 

 of Chinese ink. 



The process of fertilization has been described by Waterman (1934) 

 and will be further discussed by me in a future publication. The sperm 

 attaches to the egg within the first minute after mixing the eggs and 

 sperm, but the exceedingly large fertilization cone may not be com- 

 pletely retracted for a period of twelve to fourteen minutes. Some time 

 during the course of sperm entry, the protoplasmic processes are with- 

 drawn into the egg. The egg is too opaque to allow for the direct ob- 

 servation of any internal processes other than those connected with the 

 spindle area. 



Preceding the formation of the first and second polar bodies there is a 

 distinct flattening of the egg at the region where the polar bodies will 

 be extruded. The first polar body separates at about nineteen to twenty- 

 three minutes after fertilization; the second comes off nine to eleven 

 minutes later. At fifty to fifty-five minutes after fertilization, a large 

 anti-polar lobe is formed and the cell divides into two (sixty-five to 

 seventy minutes) . After the division the polar lobe goes into the CD cell. 

 Ten to fifteen minutes later, a smaller lobe is given off at the anti- 

 polar end of the CD cell and the second cleavage occurs. At the com- 

 pletion of the division the lobe flows into the D cell. The first set of 

 micromeres, which are only slightly smaller than the basal cells, comes 

 off in the usual dexiotropic fashion. During the course of this division 

 a third lobe forms in the D cell. The later cleavage has not yet been 

 described. 



At five and a half hours, the developing embryo begins to move about 

 by means of cilia and at eight hours the apical tuft and prototroch are 

 well formed. The larvae live fairly well on a diet of the diatom Nitzs- 

 chia. One larva was raised, without much care, to the beginning of meta- 

 morphosis (seven weeks) at which time it was fixed. Wilson (1929) has 

 given a detailed description of the larvae of the British Sabellarians with 

 which those of Sabellaria vulgaris agree very closely. 



The exact time relations in development and the effect of change of 

 temperature on such relations have not been studied. The schedule of 

 events as given above is only approximate for room temperatures 

 varying from nineteen to twenty-five degrees C. 



