STRUCTURE AND DEVELOPMENTAL RATE 199 



developed, except that in one or two of the cases one component 

 is more decidedly twisted than the other. This twisted condition 

 in some cases causes one component to appear considerably 

 larger than the other. This, however, is only an appearance, 

 -and examination of the actual specimen shows the components to 

 be very closely equal in size. 



Correctly speaking, none of these components are structurally 

 deformed. The application of the term 'double monster' to such 

 individuals as these is actually a misnomer, since there is nothing 

 whatever deformed or monstrous about their structures. The 

 condition of being double is a perfectly normal result of the growth 

 of two buds from a single stock. However, these individuals 

 have arisen from unusual conditions acting on the developing egg 

 during a particular interval and exhibit, therefore, unusual and 

 modified developmental results. Similar conditions affecting 

 other developmental periods are responsible for the production 

 of all types of structural deformities and so-called monsters. 

 The double series is, therefore, similar in so far as its causal origin 

 goes to the ordinary monstrous forms, yet one could scarcely 

 term two perfectly developed identical twins such as those shown 

 by the last specimen of the series as monsters. 



A study of the series here illustrated in addition to a large num- 

 ber of similar double specimens not only of fish, but of other ani- 

 mals as well as man, leads to the general conclusion that, When 

 the two components of a double individual are equal in size they are 

 both normal in structure. This means simply that such compo- 

 nents are as strongly inclined to be normal as is a single individual 

 and not that they are never deformed. All figures of double 

 specimens in the literature furtheii illustrate this point. One 

 may deduce from these facts that if there was a competition of 

 any kind between two such components, the advantages of each 

 in the struggle have been equal. When the advantages are un- 

 equal, it will be found that a very different state of affairs results. 



