THE CONCEPTION OF LIFE III 



tion that protoplasm, in spite of the fact that so far as we can 

 observe it propagates itself and in this propagation remains 

 like itself, nevertheless alters in the course of time. The 

 continuous, slowly progressive change of protoplasm which 

 has led to the origin of species, we designate as the phylogen- 

 etic variation. Many experiments on variation have been 

 made in recent years. In one direction our knowledge has 

 been greatly extended. The so-called Mendelian variation 

 is certainly known to you. It is rema,rkable that the varia- 

 tions which have been found in the investigation of the Men- 

 deUan law are not new variations, but on the contrary in 

 such cases as have hitherto been analyzed with certainty, we 

 have to do with the dropping out of a character. This is 

 illustrated by the beautiful experiments of Professor Morgan^ ^ 

 of Columbia University on Drosophila. The eyes of this 

 small fly vary in their color. Morgan has succeeded in prov- 

 ing by his experiments that four factors determine the color 

 of the eye, and that all variations in the color are caused by 

 the dropping out of one or more of these factors. The varia- 

 tions arise by the exclusion of a character which is present in 

 normal individuals. We stiU have to discover the origin of 

 new variations, although we have already some indications of 

 the answer to this problem. I shovild like to discuss the mat- 

 ter if time permitted, but I must restrict myself to a single 

 example. Professor Stockard^* has made experiments at the 

 Biological Station at Woods Hole, which led him to the fine 

 discovery that the addition of minute quantities of magnesium 

 chloride to ordinary sea water creates some wonderful modi- 

 fications in the development of bony fishes. He employed 

 for his experiments Fundulus heterochtus, a species of minnow 

 very common at Woods Hole. Eggs which are kept in the 

 magnesium water produce embryos which appear normal in 



