ARTIFICIAL MONSTROSITIES 157 



which are well known not to be inherited. They are merely 

 distortions, effected by easily recognizable mechanical agencies. 



Much more remarkable and difficult to understand are those 

 cases in which the addition of specific chemical reagents to the 

 water in which aquatic larvae are developing produces such 

 definite and extensive modifications of structure as to give rise to 

 veritable monstrosities. The "Lithium larva?" of sea-urchins and 

 frogs have long been known and more recently Stockard has 

 described 1 the "Magnesium larva" of the fish Fundidtis hetero- 

 clitus (Fig. 75). He found that, when the developing embryos 

 of this fish are subjected to the influence of magnesium salts 

 dissolved in sea water, a large percentage of them acquire a 

 " cyclopean " character, with a single median eye in place of the 

 ordinary pair. Such embryos may hatch and swim about in a 

 perfectly normal manner, but it is not known whether they can 

 be reared to the adult condition. These observations seem to 

 indicate that the cyclopean monsters which sometimes occur in 

 man and other mammals may also be somatogenic variations due 

 to some unknown environmental influence. 



Blastogenic or Germinal Variations. In this category are included 

 those variations which are believed to owe their origin to some 

 modification in the germ cells from which the organism 

 exhibiting them has developed. 



It is important to observe that the term congenital, sometimes 

 used in this connection, is not synonymous with blastogenic, for it 

 is obvious that animals which, like the mammalia, remain within 

 the womb of the mother during the early stages of development, 

 may come to develop purely somatogenic characters before birth, 

 due to environmental influences acting in utero (e.g. poisoning of 

 the fffitus due to parental alcoholism). 



It is very doubtful, as we have already said, whether we 

 can really draw any absolute distinction between blastogenic 

 and somatogenic characters, and it seems by no means impos- 

 sible that somatogenic modifications may sooner or later 

 make an impression upon the germ cells and thus ultimately 

 become blastogenic. This point, however, will be discussed 

 later on. 



Blastogenic modifications are from their very nature as 

 attributes of the germ cells handed on by heredity from gene- 

 ration to generation. All true mutations must be regarded as 



1 " Journal of Experimental Zoology," February, 1909. 



