406 THE MAINTENANCE OF SPECIES 



wonder to the biologist. Another interesting study centers about 

 the development of the various protective devices that surround the 

 embryo and keep it from injury until it is hatched or born. The 

 infinite care with which these devices have been developed is a credit 

 to the ingenuity of Mother Nature. 



In this unit the student will find the answer to questions arising 

 in his mind concerning the nature of these reproductive devices. 



Where Did Life Come From? 



Greek and Roman literature is full of references to the possible 

 origin of life and to the probability that it arose spontaneously. A few 

 brave souls dared to doubt this almost universally accepted concept. 

 However, even as late as the 17th century Alexander Ross writes, 



"So may we doubt whether in cheese and timber worms are generated, 

 or if beetles and wasps in cow-dung, or if butterflies, locusts, shellfish, 

 snails, eels, and such life be procreated of putrefied matter, which is to 

 receive the form of that creature to which it is by formative power disposed. 

 To question this is to question reason, sense, and experience. If he doubts 

 this, let him go to Egypt, and there he will find the fields swarming with 

 mice begot of the mud of Nylus, to the great calamity of the inhabitants." 



Refutation of Spontaneous Generation 



Belief in spontaneous generation was first shaken by the Italian 

 physician Redi, who noticed that flies were attracted to decaying 

 meat. In an experiment he put sterilized meat into several jars, 

 covered one lot with parchment, another lot with a fine netting, and 

 the third he left open. Fly maggots were found later in the meat 

 in the open jars, fly eggs on the netting, and no maggots in the parch- 

 ment-covered jars. This experiment should have exploded the belief 

 that maggots arose spontaneously from rotting meat. However, 

 the belief kept constantly recurring because it was very difficult to 

 prevent the invasion of food materials by bacteria, even after the 

 substances and vessels containing them were apparently sterilized. 

 The Abbe Needham, seventy years after the Redi demonstration, 

 experimented with living germs, and because of the errors arising from 

 improper sterilization found living germs in flasks of nutritive fluid 

 that had first been heated and then were sealed with a resinous 

 cement. A little later the Itahan, Spallanzani (1729-1799), placed 

 nutrient fluids, such as meat and vegetable juices, in glass flasks, the 

 necks of which were sealed in a flame ; then he placed the flasks in 



