bulletin: museum of comparative zoology. 



III. Methods. 



The killing fluids used were (1) 10% forniol, (2) Flcmming's stronger 

 fluid, (3) Vom Rath's picro-sublimate mixture, (4) bichromate of po- 

 tassium, (5) Gilson's fluid, arranged in the order of their value. I failed 

 to get successful preparations with Vom Rath's platinic chloride mix- 

 ture. Where decalcification was necessary Flcmming's mixture gave 

 very good results. The usual methods of further procedure for sections 

 by the parafiiu process were used. Heidcuhain's iron hematoxylin gave 

 the best stain, though Delafield's and Ehrlich's hajmatoxylins also gave 

 successful preparations. These were followed by Congo red or acid 

 fuchsin to differentiate fibre tracts. The acid fuchsin has the further 

 advantage that it stains developing bone and fibrous connective tissue. 

 The Weigert stain with copper and the Weigert-Pal method were both 

 used in nerve study. Both adult brains and the larva) proved to be 

 refractory material for the Golgi method. The rapid method was used, 

 but not more than 5 per cent of the specimens gave any impregnation 

 whatever. A sojourn of three days in the Golgi fluid and more than 

 two in the silver bath were found to give the most successful prepara- 

 tions. Material was left in the silver until wanted for sectioning, 

 though much of it was sectioned after an exposure of two days to the 

 silver nitrate. 



IV- Migration of the Eye and Changes in the 

 Cartilaginous Skull. 



Before proceeding to describe the conditions which I have found in 

 Pscudopleuronectes americanus, I shall give a brief account of the main 

 results reached by previous observers, omitting for the present those of 

 Pfcffer. 



1. Summary of Previous Studies on the Migration 



OF THE Eye. 



It was suggested about the middle of the last century, that the Plcu- 

 roncctidaj, though unsymmetrical as adults, are, in their young stages, 

 bilateral animals like other fish. The brief accounts of Van Beneden 

 ('53) and Malm ('54), who found young fish quite similar in markings 

 to adult flatfishes, but with eyes in a different position, seemed to indi- 

 cate the possibility that one of the eyes migrated around the head from 

 one side to the other. 



