FERTILIZATION IN PLATYNEREIS MEGALOPS. Ill 



clear that the spermatozoa behave in abnormal fashion even 

 granting that I may have overlooked the amphiaster. The 

 evidence seems to indicate that after sea-water treatment the 

 egg lacks the power to engulf the sperm. However, whatever 

 the method of penetration one point is beyond contradiction: 

 these washed eggs never cleave. 



The observations agree with those of Lillie ('14) who notes 

 that some unpublished observations in the case of Nereis show 

 that "if the cortical changes be induced by artificial means there 

 is a brief period in which insemination of the eggs may be followed 

 by penetration of the spermatozoon, but without causing cleavage 

 of the egg." Miss AUyn found that after KCl treatment of the 

 egg of Chcstopterus , the spermatozoon may enter but its behavior 

 is not normal. Kite (quoted from Lillie '14) finds that sper- 

 matozoa injected into star-fish eggs never give cleavage. 



In these cases, the interpretation must be that the "fertiliz- 

 able" condition of the egg has been destroyed through loss of 

 fertilizin before insemination. In the same way sperm may pene- 

 trate unripe eggs as Hempelmann has shown for Saccocirrus (so 

 too, von Hofsten for Otomesostoma and Shearer for Dinophilus gyro- 

 ciliatus) . Two years ago I found that eggs from Nereis limbata just 

 before transformation into the heteronereis phase would not fer- 

 tilize with active sperm either from the nereis or he ceroneris form. 

 Moreover, eggs from metamorphosing worms kept for several 

 weeks in the laboratory although apparently ripe would not 

 fertilize on insemination during the dark of the moon. At full 

 moon, sometimes but a few days later, eggs from the same animal 

 would fertilize and develop into larvae which were kept for weeks. 

 We may assume in these cases that the fertilizin is either absent 

 or is unavailable. Penetration, therefore, may take place before 

 the fertilizable period is reached as well as after it has been 

 passed, but the egg is not capable of fertilization. 



3. Apposition of the germ nuclei of Platynereis after sea-water 

 insemination may ensue, but never cleavage. After the loss of 

 the fertilizing substance, then, the normal fertilization process 

 may be closely simulated even to the point of the copulation of 

 the pronuclei but development never goes beyond this point. 

 In short, the normal fertilization process demands at the very 



