CHAPTER TEN 

 EGGS AND SPERMS. 



1. Conjugation the Starting Point. There have been 

 no differences in the gametes or mating bodies in those 

 species we have studied. The ciliated gametes of Ulothrix 

 are of the same size and structure. The mating cells of 

 Spirogyra are apparently alike. The paramecia that unite 

 are as nearly alike as it is possible for organisms to be. 

 Indeed, we call the process conjugation only when the 

 gametes are alike, so far as we can perceive. This 

 condition must be looked upon as the simplest kind of 

 union of offspring. It seems to be the beginning of a 

 process which is very common in both plants and c.nimals. 

 This we must now study. 



2. Beginning of Differences in Gametes. Pandorina 

 is a simple green plant made up, when mature, of sixteen 

 cells held together by a jelly which they have secreted. 

 It is not a plant you are likely to see, but it is 

 described in both botanies and zoologies, because it is 

 hard to say whether it is more like plants or animals. It 

 starts as a single cell. By a series of divisions the mature 

 colony of sixteen cells is finally formed. Any one of these 

 sixteen cells may start a new colony by dividing again. 

 Or, instead of this, any one or all of these cells may 

 divide into a number of gametes, which are small and 

 ciliated. These escape from the jelly into the water and 

 unite in pairs. The gametes are almost alike, but differ 

 more or less in size. A smaller and a larger unite. 



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