Artificially Produced Cyclopean Fish 299 



their tails caused no excitement. In two instances they hved 

 for ten days, which is about as long as the two-eyed embryos can 

 survive without food. At this time the entire content of the yolk- 

 sac has been absorbed. The embryos in nature doubtless begin 

 feeding previous to this stage. The cyclopean individuals appear 

 to be as active as the normal and their ability to live would seem 

 to depend only upon the possibility of their obtaining food. 



A normal fish eight days after hatching is illustrated by Fig. 23. 

 The mouth projects forward beyond the dorsal tip of the head 

 and the two eyes are lateral in position. A cyclopean embryo 

 eight days after hatching is shown in Fig. 24. Here the two eyes 

 are united and occupy the position which the mouth has in Fig. 

 23. In Fig. 25 a perfectly cyclopean eye is shown in dorsal view: 

 the same individual is seen in lateral and ventral views in 

 Figs. 26 and 27. This fish swam in a normal manner. In the 

 lateral position the mouth is shown projecting ventrally as a pro- 

 boscis-like structure. This condition is due to the fact that the 

 single antero-median eye occupies the position normally assumed 

 by the mouth and thus obstructs the usual forward growth of its 

 structures. The mouth, therefore, remains ventro-posterior to the 

 eye and grows downward, presenting the proboscis-like appearance. 



Such a condition recalls in a striking way the nose of the mam- 

 malian Cyclops. In mammals the cyclopean defect is accom- 

 panied by a proboscis-like nose situated in the forehead above the 

 median eye. The nose in normal development grows downward 

 to its facial position, but in cyclopia the median eye obstructs its 

 path and forces the formation of the proboscis-like organ in the 

 forehead. The same explanation holds for the fish's mouth 

 where the eye prevents its forward growth, producing the proboscis- 

 like organ. 



It is interesting to find that the mouth in cyclopean fish stands 

 in a position so as to fall in the gill series as number one, all the 

 gills and the mouth have the same general direction. I have 

 found that in Bdellostoma the mouth arises in a manner similar 

 to the gills and actually at first arches dorsally and only secondarily 

 arches ventrally. It may have originally been a member of the 

 gill series, as Dohrn (1875) ^^^ ^^^§ thought. It would be 



