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An Interesting Abnormality 

 LESLIE TA5CHE 



Zoological Laboratory), UniOersitj) of Wisconsin 





Yellow Perch, Perca flavesens, Showing Two Ani 

 Photograph by A. S. Pearse 



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The abnormal has always been inter- 

 esting. Normal structure, although in- 

 teresting from a purely scientific stand- 

 point, fails to attract the attention of the 

 average man. It is too commonplace. 

 The abnormal - on the contrary is made 

 conspicuous by its noticeable dissimilar- 

 ity to the normal. People since the be- 

 ginning of time have preserved and ex- 

 hibited every variety of unnatural forms. 

 "Freaks of Nature," as they are called, 

 and have wondered at their origin and 

 development. During the early periods 

 of civilization there was a great deal of 

 superstition connected with many of 

 these malformations. Many forms were 

 feared and great reverence was extended 

 to them, because they were thought to be 

 the work of spirits, others were used as 

 charms for luck and for medicinal pur- 

 poses, but most of them were kept mere- 

 ly because they were different. As civ- 

 ilization advanced, most of these super- 

 stitious views were discredited and men 

 began to examine them scientifically as to 

 origin and development ; but to this day 

 people of many classes still believe in 

 the supernatural powers of some of the 



types and everybody is more or less in- 

 terested in any striking malformation 

 that is put on exhibition. Scientific in- 

 vestigations have shown that these forms 

 are the result of unnatural embryological 

 development or the product of patho- 

 logical changes in the growth of parts of 

 the body in respect to size, shape, posi- 

 tion, or number. 



An example of one of these "Freaks 

 of Nature" is found in a yellow perch, 

 Perca flavesens (Mitchill) : the presence 

 of two ani situated exactly on the me- 

 dian line. The fish was caught on No- 

 vember 23, 1917, in Lake Mendota near 

 Madison, Wisconsin. It was normal in 

 size, measuring 16.1 centimeters in 

 length, and apparently in good condition. 

 The presence of two ani came to the no- 

 tice of Professor A. S. Pearse while he 

 was preparing to dissect the fish in order 

 to determine what it had eaten, and he 

 took the accompanying photograph. 



The presence of two ani in the Class 

 Pisces is not a very rare thing by any 

 means, but such openings are usually 

 paired ; one to the right and one to the 

 left of the median line, usually at right 



