THE PINEAL BODY 223 



far come under observation, the differentiation in the pineal 

 body has been in the interest of glandular formation. This 

 evidence is not alone to be found in the character of the cells 

 which compose the body, but even more in the arrangement of 

 these cells whose alveolar patterns constitute irrefutable reasons 

 for regarding the epiphysis as a true gland in birds. 



Three types of this gland are found in the avian forms, namely, 

 1) the tubular type, in which the secretion is delivered to the 

 ventricular system; 2) the endocrinic type, in which the secre- 

 tion reaches the blood stream, and 3), a mixed type, partaking 

 of the character of each of the former varieties. This evidence 

 afforded by birds is so conclusively in favor of the glandular 

 nature of the epiphysis as to leave no grounds for dispute. 



Histological evidence in mammals. It is perhaps in mammals 

 that the most extensive observations have been made with 

 reference to the histology of the pineal body. Indeed, it is in 

 these animals that the greatest variety of opinion has been 

 expressed. It would seem advisable to take into account these 

 different views concerning the histological character of the organ. 

 A large group of investigators adheres to the belief that the 

 pineal body is a blood vascular gland. This group includes, 

 among others, Valentin, 403 Faivre, 114 Leydig, 231 Bizzozero, 31 

 Galeotti, 140 Constantini, 71 Cutore, 76 Galasescu-Urechia, 137 

 Krabbe, 217 Biondi, 49 and Kidd. 203 Jordan, 199 although he does 

 not advocate the improbability of glandular formation, believes 

 that the organ is essentially neural in its structure. 



Several investigators maintain that the epiphysis in mammals 

 consists exclusively of neuroglia. Among these are Cionini, 66 

 Edinger, 103 and Weigert. 418 Mihalkovicz 274 believed that the 

 cellular consistency of the pineal body in mammals was exclu- 

 sively of the ependymal type. Those of another group assert 

 that the epiphysis resembles a lymph gland. Of this opinion are 

 Schwalbe, 348 Henle, 171 Ellenberger 110 Mingazzini, 276 and Lord. 249 



Although it has been frequently claimed by many writers 

 among both the early and recent workers in this field that the 

 epiphysis is a vestige, it is interesting to note that no suggestion 

 of such a possibility is made by any of the authorities just 



