FERTILIZATION REACTION IN ECHINARACHNIUS PARMA. 3 



completely activated can not respond to additional insemination; 

 and fragments of inseminated eggs behave similarly. 



Through the well-known experiments of the Hertwigs, Boveri, 

 Morgan, and others it has been shown that enucleated fragments 

 from uninseminated eggs of sea-urchins are fertilizable as are 

 nucleated fragments. Wilson has shown that the enucleated frag- 

 ments taken from the egg of Cerebratulus after dissolution of the 

 germinal vesicle are fertilizable. In a very cautiously worded 

 paper appearing posthumously Boveri maintained his original posi- 

 tion as to the fertilizability of enucleated fragments of uninsemi- 

 nated eggs. 



I find that fragments from uninseminated eggs of Echina- 

 rachnius obtained by gently shaking the eggs in a vial with bits of 

 a broken coverslip are capable of fertilization and development. 

 The development of these fragments does not depend upon the 

 presence of the egg nucleus. Some fragments without egg nuclei 

 fail to respond to insemination. A fragment of large size and 

 with a nucleus may not fertilize. Very small fragments with no 

 egg nucleus develop. / believe that the failure of fragments to 

 fertilise is due to the absence of cortical material. This belief is 

 based on results which may now be considered. 



III. 



Toward the end of the season of 19 17 I frequently found that 

 fertilized eggs of the Echinarachnius gave rise to abnormal gas- 

 trulse which I took to be ordinary exogastrulae. They prove to be 

 gastrulse with masses of undifferentiated protoplasm attached. 1 

 The breaking up of these masses simulates cleavage. A careful 

 study of these eggs was made and the history of this condition 

 revealed. 



I found that among various lots of eggs kept for some time in 

 shallow dishes with little sea-water were some eggs which on 

 return to a larger quantity of normal sea-water underwent a frag- 

 mentation. Under the microscope this process is easily followed. 

 The eggs give off a bud or form an exovate that slowly increases 

 in size and drops off. Thus in a given lot of eggs there are in- 



1 These masses are always located at the vegetative pole. This may be 

 significant for the problem of polarity. 



