CHAPTER V 



DOUBLE MONSTERS OR CONJOINED TWINS 

 IN FISHES 



CLASSIFICATION AND ANATOMICAL STRUCTURE 

 OF CONJOINED TWINS 



The earliest adequate classification of conjoined 

 fish twins is that of Windle (1895), who concerns himself 

 only with the external evidences of duplicity. He 

 recognizes eleven classes of trout twins characterized 

 by the following structural peculiarities : 



1. Three eyes of the same size (the least manifestation 

 of duplicity noted by any of the authors). 



2. Three eyes, the median being larger than either 

 of the lateral ones. 



3. Four equal-sized eyes. 



4. Two heads, the duplicity extending as far back 

 as the otic region. 



5. Duplicity extends to the region of the pectoral fins. 



6. Duplicity extends to the posterior border of the 

 yolk sac, the caudal extremity of the fishes being quite 

 single. 



7. Duplicity extends a short distance behind the 

 posterior border of the yolk sac, but the caudal extremity 

 is quite single. 



8. Duplicity extends to the posterior border of the 

 yolk sac. Behind this there are two caudal extremities 

 overlapping one the other and firmly united by their 

 contiguous aspects. 



SI 



