THE FERTILIZATION-PROCESS 



The statement made in the chapter, Life and Experi- 

 ment, that we lack many details concerning the happenings 

 in normal biological processes, can be proved when the 

 history of fertilization in the various examples given below 

 is reviewed. Although I have endeavored to choose a 

 representative for each class whose fertilization is best 

 known, we shall see that in no one have all the steps been 

 completely followed. Fertilization is far from being a 

 sterile field of research; there is no single animal egg for 

 which the events, from the moment of contact of egg and 

 spermatozoon to first cleavage, have been so adequately 

 described in closely set stages that we can say that we pos- 

 sess full information of the chain of events as a continuous 

 process. The description of fertilization in four eggs, that 

 now follows, will give us merely the chief outlines of a pic- 

 ture which we shall try to make more complete by adding 

 lines and details from the process in other eggs. Only 

 then shall we draw conclusions and enter upon the discus- 

 sion of fertilization. 



I describe fertilization as it occurs in the egg of Nereis 

 limbata found along the Atlantic shores of America; it 

 represents eggs of Class i.^ 



The fertilization of the egg of this easily obtainable 

 marine worm can be controlled since the eggs are discharged 

 freely into the sea where they are immediately mixed with 

 the spermatozoa; one needs merely to collect the mature 

 males and females separately and then to place them 

 together in pairs at timed intervals to obtain fertilized eggs 

 in a series of as closely set stages as one desires. One 

 draw-back exists, namely, that sexually mature animals 

 can not be found throughout the summer months when the 



^ This account is based in large part on that given by L^llte, igil 

 and IC)I2. 



