8 THE PINEAL ORGAN 



In recent years the interest shown in the pineal body has been revived, 

 more especially in connection with its supposed endocrine function. 

 This has led to a more exact study of its histological structure and experi- 

 mental work on animals along the lines of extirpation, feeding with the 

 whole gland or desiccated preparations of the gland, injection of extracts, 

 and grafts. Details of this work will be discussed later, it being only 

 necessary to mention here that although much has been learned by the 

 use of special neurological methods of histological technique and from the 

 clinical observations of pathological cases occurring in the human subject, 

 the results recorded by various authors of the experimental work are often 

 conflicting, and the clinical syndrome described by Pellizzi, namely 

 macrogenitosomia precox, does not always accompany destructive lesions 

 of the pineal body, and the symptoms have sometimes been present but 

 on post-mortem examination no abnormality of the pineal has been 

 discovered. On the other hand, the careful observation and record of the 

 special pressure-symptoms which are produced by enlargement of the 

 pineal organ, accompanied by X-ray examination, has been of great value 

 in the diagnosis of tumours originating in or near the gland. 



Significance of the Pineal Body, considered from the Standpoint of 

 Comparative Anatomy 



Towards the end of the nineteenth century the opinion expressed by 

 Dendy, Gaskell, Patten, and others, that the pineal eye of vertebrates 

 was primarily bilateral in origin, led not only to further work on the pineal 

 eye of vertebrates but also to a careful comparative study of the position 

 and microscopical structure of the median (paired and unpaired) eyes of 

 invertebrates ; and it was considered by Gaskell that the pineal system 

 formed one of the most important clues to the origin of the vertebrates. 

 These, he believed, originated from a pre-vertebrate ancestor which had 

 affinities with one of the higher invertebrate phyla, and more particularly 

 the Arthropoda. The similarity in general form of certain fossil fishes 

 belonging to the class Ostracodermi — e.g. Cephalaspis and Pteraspis — to 

 the living representatives of the Xiphosura, namely the king crabs (Limulus 

 polyphemus), and also to some small living crustaceans, e.g. Apus cancri- 

 formis and Lepidurus, seemed to indicate that the whole vertebrate stock 

 had arisen from a remote fish-like ancestor which was related to the 

 arthropods and more particularly to the Xiphosura, Trilobites, and the 

 gigantic " sea scorpions " Eurypterus and Pterygotus. Recent embryo- 

 logical and palacontological work has, as we shall show later, done much 

 to confirm the view that the pineal organ was primarily a bilateral structure, 

 but it is now believed that the vertebrate stock branched off from the 



