214 BIOLOGY 



necessary consciousness on its part, as actually happens in 

 sleep, for example. Such an action is called a reflex act, a 

 name derived from the idea formerly held that the impulse 

 starting from the sense organ was simply reflected back after 

 reaching the cord. Although we know to-day that the impulse 

 is not simply reflected back, but is profoundly modified in the 

 cord, the name reflex is still retained for this type of reaction. 



Although a reflex act is not necessarily accompanied by con- 

 sciousness or sensation, this is not always the case. From the 

 diagram (Fig. 103), it is evident that the impulse, on its arrival 

 in the cord, may not all pass into the motor nerve cell, but some 

 of it may pass up through the fiber, a, toward the brain, and this 

 part of the impulse, when it reaches the brain, will give rise 

 to a sensation. The action that follows might still be the 

 reflex, or it might be a truly voluntary one, started by the brain 

 as the result of the sensation. Reflexes play a very large part 

 in the life of all animals. Even in our own life many of our 

 actions are thus reflexly performed without any special volition. 



Reproduction. The eggs of the frog are only developed at 

 certain seasons of the year. Late in the spring and early in the 

 summer the ovaries are small, but toward the end of summer 

 and in the fall the eggs begin to develop and cause the ovaries 

 to expand until they almost fill the body cavity. When the 

 frog goes into the dormant condition of hibernation (Lat. 

 hibernare = to pass the winter), the female is usually greatly 

 distended with the swollen ovary, and in this condition the 

 winter period is passed. The oviducts have also enlarged and 

 elongated, and remain so during the winter, while the animal 

 is buried under ground. With the opening of the spring the frog 

 emerges and resumes its active life, and in a few weeks reaches 

 what is called the breeding season, which means the season 

 for the discharge of the sexual products. As this season ap- 

 proaches the eggs break out of the ovary and fall into the 

 abdominal cavity. The funnel-shaped opening of each oviduct 

 is provided with vibratile cilia (Fig. 100), and, probably by 



