No. 627] GERM PLASM OF THE OSTRICH 321 



internal physiological causes or to extraordinarj^ environ- 

 mental stresses acting upon the germ cells. We have 

 already seen that germinally the Soutli African osti i<']i is 

 most irresponsive to any environmental diaiiuv- and we 

 have no reason to suspect that its nortlin n relative is in 

 any way more impressionable. In the climatic and other 

 environmental conditions of North Africa it is difficult to 

 conceive of anything which could, for example, modify the 

 bodily colors as compared with those of the southern bird, 

 or could bring about a perfectly smooth round egg in con- 

 trast with an oval pitted one, much less which could either 

 directly or through the soma change the germ cells so as 

 to render the differences hereditary. Of course we know 

 next to nothing of the influence upon the germ cells of 

 extraordinary environmental stresses and to labor the 

 point would be unprofitable. But doubt may certainly be 

 expressed as to w^iether any external influence could so 

 change them as to bring about the formation of a bald 

 head patch, a feature which it is impossible to regard as 

 having an adaptive significance. It is a new germinal 

 character which has appeared in the northern bird, en- 

 tirely sui generis; there is nothing suggestive of it in the 

 southern ostrich. 



We have the hard fact to account for that the germ 

 plasms of the northern and the southern ostrich differ 

 from one another in certain respects as revealed by their 

 manifestation in the soma, and it is also proved that they 

 breed true irrespective of environment. And while in our 

 condition of absolute ignorance no good purpose will be 

 served by dogmatizing it may be permitted to express the 

 conviction that the germ plasm changes as between the 

 northern and southern ostrich have resulted entirely from 

 internal physiological causes. The conviction is strength- 

 ened all the more from the facts to be presented in the 

 next section. 



