NATURAL HISTORY OF CU.MIXGIA TELLIXOIDES. 211 



or more of the egg secretions that Lillie has shown to be concerned 

 with the fertilization reaction in the Xereis egg, and which sweep 

 supernumerary spermatozoa from the surface of the egg after 

 the initiation of the fertilization reaction. It frequently happens 

 that one can count ten or a dozen sperm nuclei w r ithin an egg that 

 has been too heavily inseminated. Cases have been seen in which 

 every egg showed polyspermy of this extreme character. \Yhen 

 eggs are spawned the germinal vesicle has already broken down 

 and the first polar spindle has formed. On this account the first 

 polar body appears very promptly after insemination. 



Morgan found that the egg of Cumingia is very easily injured 

 by rough handling so that it may fail to develop normally 

 beyond cleavage. At first he was unable to secure normal 

 veliger larvae from centrifuged eggs. He finally centrifuged the 

 entire animal before it had spawned and, to his surprise, it 

 spawned completely centrifuged eggs which developed normally, 

 showing that the dislocation of the egg materials did not interfere 

 with normal development. He came to the conclusion that the 

 trouble he had experienced was due to injury to the membranes 

 of the egg. 



RATE OF GROWTH, METAMORPHOSIS AXD LIFE HISTORY. 



The polar body is of interest chiefly because of its great size 

 and mode of formation. It seems to round up before it comes to 

 the surface of the egg and to migrate out, breaking its way 

 through the cytoplasm of the egg as the latter is pushed up into 

 a rounded prominence. The vitelline membrane, being thick 

 and elastic, is pushed up locally. As a curious anomaly, no 

 doubt associated with polyspermy, one case was observed in 

 which two polar bodies came off at the same time, side by side, 

 and were followed after the usual interval by a third polar body. 

 As a rule only two polar bodies are formed. The first one 

 rarely divides, although its division has been observed now and 

 then. In case of polyspermy the cell may go into the three- 

 celled condition at the first cleavage, and the polyspermic 

 embryos may be normal or abnormal. Cumingia would, in fact, 

 be first class material for a study such as Boveri's on the 

 Echinoderm egg. 



