CHAPTER IV 



ONE-EGG TWINS IN FISHES 



INTRODUCTION 



The existence of one-egg twins and double monsters 

 in fishes has been known for a long time. Possibly the 

 earliest reference in the literature to this subject is 

 that of Aldrovandus (1642) in his Monstrorum Historia. 

 Since then probably no less than a hundred papers and 

 monographs, describing one or more specimens of fish 

 exhibiting some degree of duplicity, have been published. 

 Most of these authors have apparently been under the 

 impression that they were reporting some new and 

 strange monstrosity and their accounts have been 

 superficial. A number of them have secured considerable 

 collections of eggs containing twins or double monsters, 

 and practically the same series of monstrous types has 

 been shown to appear in all representative collections. 



As to the frequency with which twinning occurs in 

 fishes we have only a small amount of evidence. Rauber 

 found two double monsters among 1,000 trout eggs; 

 and one in 325 pike eggs; Coste found over 100 double 

 monsters in about 400,000 eggs of various species; 

 LerebouUet found 222 double monsters in 203,962 eggs 

 of the pike. The percentage of twins is so small that 

 the collection of an adequate series of specimens must 

 be a task of some moment. Among the kinds of fishes 

 in which double monsters have been described we may 

 mention the following: sharks, skates and rays, lung- 



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