1877.] On the Development of the Nerves in the Chicle. 47 



others of the family steps towards this highly specialized arrangement, 

 the benefit of which to a voracious predatory fish, such as the hake, is 

 obvious *. 



The common cod has teeth which admit of a small amount of motion 

 only ; but a comparison of them with those of the hake shows clearly that 

 a further modification in the same direction would lead to an attachment 

 similar to that of the latter fish. 



The haddock, which in this respect is a fair representative of the 

 family, has teeth which admit of no motion at all. 



III. " Note on the Early Stages of Development of the Nerves 

 in the Chick." By A. Milnes Marshall, B.A., B.Sc, of 

 St. John's College, Cambridge. Communicated by Dr. 

 Michael Foster, F.R.S., Prelector of Physiology in Trinity 

 College, Cambridge. Received February 13, 1877. 



In the investigations here described embryos of ages from thirty-six 

 hours to four days were employed. These were, for the most part, 

 hardened by immersion in picric acid, prepared after Kleinenberg's 

 method, for three to five hours, and then in alcohol of gradually increasing 

 strength. It is to the use of picric acid as a hardening agent that the 

 results obtained are believed to be in large measure due. All the more 

 important results have, however, been confirmed by specimens hardened 

 in chromic acid in the usual manner, though such specimens have 

 almost invariably proved inferior in distinctness to those prepared with 

 picric acid. Good results have also been obtained from duck-embryos 

 hardened in picric acid. 



Owing to the less compact character of the mesoblast of the head and 

 to the absence of proto vertebrae, the development of the cranial nerves is 

 easier to study than that of the spinal, and will therefore be considered 

 first. 



Transverse sections through the hind brain of a forty-three hours' 

 chick show that the cells along the median dorsal line are more spherical 

 in shape and slightly smaller than those composing the rest of the brain ; 

 also that these spherical cells grow upwards, so as to form a conspicuous 

 longitudinal ridge running along the upper surface of the hind brain 

 immediately beneath the external epiblast. 



This ridge is traceable along the whole length of the hind brain, but is 

 much more prominent posteriorly than it is in front, where it gradually 

 disappears. At intervals the ridge becomes more prominent, and grows 



* Since the accompanying paper was placed in the hands of the Eoyal Society, the 

 author has found that the vomerine and palatine teeth of the pike present a similar 

 hinged manner of attachment, so that they oppose no obstacle to the swallowing of 

 prey seized by the fish. 



