302 Descriptive Zoology. 



Development of Metazoa. Every metazoan begins life 

 as a single cell (except in multiplication by budding). It 

 starts as an egg (ovum or egg cell;, having very much 

 the same characteristics as an amoeba. After being fer- 

 tilized it soon divides into two parts, but these halves, 

 instead of separating, as' in the case of the amoeba, re- 

 main together. These halves divide into quarters, and. 

 so on, into 8, 16, 32, 64, 128, etc., parts, until they become 

 too numerous to be counted. Aft'er a time these numer- 

 ous cells, still remaining together, arrange themselves in 

 the shape of the animal that produced the egg cell. 



Division of Labor in Communities. A solitary back- 

 woodsman has to do everything for himself. He gets and 

 prepares his own food, provides needed shelter, makes his 

 own clothing. But if he has a partner, there is sure to be 

 some division of their labor. One can do some things 

 better than the other, and they find that it is advantageous 

 for each to do what he can do best. In an Indian family 

 the men do the hunting and fighting, while the squaws pre- 

 pare the food, dress the hides for clothing and lodges, etc. 

 It is hardly necessary to call attention to the saving of time 

 that results from such a division of labor, or to note the finer 

 quality and finish of the various articles of common use 

 when they are made by one who acquires skill by the con- 

 stant practice which comes from devoting himself entirely to 

 one kind of work. It is evident that no one man can do many 

 things and do them all as well as when the work is divided. 



Physiological Division of Labor. An amoeba does every- 

 thing for itself. Of course it lives very well in its simple 

 way, and is well adapted to its mode and place of life. 

 But it does too many things to do any of them very well. 

 It can move but slowly, it is dull of sensation, etc. Su] 

 pose that, when an amoeba divides, the two parts remaii 



