112 



Dr. J. Beard. 



[May 16, 



non-nervous, and epithelial in character, as in Marsipobranchs, 

 Teleostei, and other Ganoids (Acipenser, Polypterus, and Amid). 



The nervous elements of the fore-brain are represented by thick 

 basal and lateral structures of a solid nature, forming the so-called 

 " corpora striata." To what extent they are homologous with 

 corpora striata shall be discussed in my full paper. To my mind 

 there appears to be no evidence to show that the fore-brain region of 

 Marsipobranchii, Teleostei, or Granoidei is a degenerate structure. 

 The pineal gland and the nervous part of the pituitary body or 

 hypophysis cerebri have the usual mode of formation. In the adult, 

 the pineal body arises by a hollow stalk from the roof of the 

 thalamencephalon, and it proceeds forwards over the epithelial roof 

 of the fore-brain, ending in a large simple flattened vesicle. This 

 vesicle has a striking resemblance in structure to the same organ in 

 Mijxine. It lies in a mass of adenoid tissue, which, however, is no 

 part of the pineal body. Waldschmidt's statements under this head 

 in Polypterus will require modification. 



The first development of the oral part of the hypophysis cerebri 

 is difficult of investigation, on account of the distortion produced 

 by the developing suckers. It arises as a medium solid ingrowth 

 of the formative epiblast, slightly in front of, or almost within, the 

 mouth involution. Its direction is towards the infundibulum and 

 the end of the notochord. It does not become hollowed out as in 

 many other forms. 



In the adult the hypophysis cerebri possesses a more complicated 

 structure than the same organ in Polypterus, containing as it does 

 glandular epithelium, lymphoid tissue, and degenerated nerve-cells. 

 Its duct does not persist as in Polypterus. 



Regarding the spinal cord, only one further remark need be made, 

 that is, that behind the anus it is for some time solid. 



The Nerves, Ganglia, and Peripheral Sense Organs. 



As Balfour and Parker state, the nose is formed as an invagination 

 of a certain portion of the formative epiblast. This is not remark- 

 able when we remember that no organs are formed from the outer- 

 most layer. 



The ear arises in the same way. The otoliths of Lepidosteus and 

 Salmo are formed similarly to the otoliths of Invertebrates. Certain 

 cells of the lining of the auditory vesicle become freed from the 

 epithelium, and lie loosely in the auditory cavity. They acquire a 

 position in rows just over the sensory hairs. The ceils become 

 calcified, and their nuclei disappear. 



The otoliths are probably formed by the fusion of a number of 

 these calcified bodies. 



