PROBLEM 2. How AloTd Co'iiiplex Aii'mids Reproduce 



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Frog 



Fig. 370 (above) Sperm cells froi// five kinds 

 of anmials. In ivhat respect do these five sperm 

 cells reseinble each other? 



Fig. 371 (right) These egg cells are not drawn 

 to scale, in what ways, other than in size, are 

 they alike and different? 



The male gamete, or sperm cell, is al- 

 ways very much smaller than the egg 

 cell. It is always microscopic. The cell 

 consists of little more than nucleus and 

 membrane. A tiny bit of cytoplasm is 

 around the nucleus and is drawn out into 

 a long, thin tail. Normally, this tail lashes 

 back and forth, and so propels the sperm 

 cell through any liquid. You can see 

 sperm cells if you do Exercise 3. 



Huma 



Fertilization. Fertilization can take 

 place only if the two gametes meet. 

 Among the various kinds of organisms 

 there are various ways in which this hap- 

 pens. Let us consider first a water-living 

 organism, a fish. At certain seasons, often 

 in the spring, egg cells develop in the 

 ovaries of the adult female. They be- 

 come separated from the other cells in 

 the ovaries in one or several lars^e masses. 



