xxxvi Journal of Comparative Neurology. 



Williams on the Embryology snul Neurology of the Flat-Fish.' 



Cole and Johnstone have given us an excellent account of the 

 adult anatomy of a typical flat-fish, and in this research we have a thor- 

 ough embryological examination of an American representative of the 

 same interesting group. A complete series of embryonic, larval and 

 young forms was studied histologically and the c:rania of the important 

 stages modeled in wax by Bcjrn's method and reconstructed by the 

 method of projection. 



The actual rotation of the eye is very rapid, the greater part of i^ 

 taking place in not more than three days, though extensive preparations 

 have been made for it in the orbital region for a long time previously. 

 'J'he first observed occurrence in preparation for metamorphosis is the 

 rapid resorption of the part of the supraorbital cartilage bar which lies 

 in the path of the migrating eye. The changes which take place in the 

 head of the flounder in connection with the asymmetry of the eyes alt 

 take place in the cartilaginous skull, ossification occurring only after 

 the shifting is complete. 



The "optic portion of the central nervous system" is described on 

 pages 23 to 47. A few notes, are given on the cranial nerves in gen- 

 eral. The optic nerve, optic tracts and tectum opticum are treated 

 more in detail. They present few peculiarities as compared with typ- 

 ical teleosts. Stress is laid on the importance of the nidulus corticalis. 

 (of Frit.sch and C. L. Herricr — Dachkern of Edjnger) as an asso- 

 ciation center for optic reflexes, confirming the description of C. L. 

 Herrick. On p. 47 he writes: "The nidulus corticaHs, developing 

 early, as it does, is probably one of the most effective association cen- 

 ters of the brain. Lying at the entrance to the tectum, with a strong 

 bundle of neurites running through the two niduli rotundi in the ven- 

 tral part of the brain, and with its numerous large dendrites passing 

 into layers 3 and 4 of the tectum, it should be able to connect the optic 

 sensory region with the motor areas quickly, and thus account for the 

 extreme rapidity of movement of these larvae." It appears probable 

 that this nucleus is the same as that described by Sargeni' as giving; 

 rise to Reissner's fiber, as intimated by Johnston in his Acipenser 

 paper. If so. this adds another important path for optic reflexes from 

 these cells. c. j. h. 



'WiLLi.\MS, S. R. Changes Accompanying the Migration of the Eye and 

 Observations on the liactus Opticus and Tectum Opticum in Pseudopleuro- 

 nectes americanus. Bui. Mus. Comp. Zoo/., XL, i, May, 190J. 



