THE HORMONES IN HUMAN REPRODUCTION 



Fertilization of the Egg 



The fertilization of an egg by a sperm cell is one of the 

 greatest wonders of nature, an event in which magnificently 

 small fragments of animal life are driven by cosmic forces 

 toward their appointed end, the growth of a living being. As 

 a spectacle it can be compared only with an eclipse of the 

 sun, or the eruption of a volcano. If this were a rare event, 

 or if it occurred only in some distant land, our museums and 

 universities would doubtless organize expeditions to witness 

 it, and the newspapers would record its outcome with en- 

 thusiasm. It is, in fact, the most common and the nearest 

 to us of Nature's cataclysms, and yet it is very seldom 

 observed, because it occurs in a realm most people never see, 

 the region of microscopic things. It is, moreover, in most 

 animals we are likely to see, a recondite event, occurring in 

 ponds or the sea, in the forest or the earth, wherever the 

 creatures lay their eggs. In mammals and birds the fertiliza- 

 tion is hidden in the depths of the body. Nor indeed are all 

 eggs suitable for study ; they may, for example, be opaquely 

 loaded with pigment like those of the frog. Such eggs may, 

 of course, be killed and cut into thin slices for microscopic 

 study, and the process of fertilization has thus been observed 

 step by step in the prepared eggs of many species, but only 

 a few biologists ever see the whole continuous process of union 

 of a living egg with a sperm cell. 



It need not be so rare a sight, however, for anyone who will 

 go to a seaside laboratory in summer can witness it. The sea 

 urchins, starfish and sand dollars which inhabit our coasts 

 almost seem especially created to reveal the process of fer- 

 tilization with utmost clearness. While writing this chapter 

 I have before me a sketchbook made while a college student, 

 working at the U.S. Fisheries laboratory at Beaufort, North 

 Carolina, where I studied with amazement the finest of all 

 these marine eggs, those of the white sea urchin, Toxopneus- 



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