THE PINEAL BODY 25 



Of the early workers upon the selachian pineal region, Jack- 

 son and Clarke (75) 193 appear to be the first to make mention of 

 the actual pineal organs as they occur in these forms. They 

 described this region in the brain of Echinorhynus spinosus. 

 According to their description, the structure was a small pro- 

 jection extending fro'm the roof of the interbrain to the surface 

 of the skull. Ehlers 108 in 1878 gave the first detailed description 

 of the relation of these parts in Acanthias and Raia. Balfour 

 ('78) 10 in the same year described the embryological development 

 of the pineal region in selachians. Cattie ('82) 60 gave the de- 

 scription of the pineal organ in a large number of Elasmobranchs. 

 Carrington ('90) 58 described the organ in Larnna cornubica and 

 Galeotti ('96) 14 employing certain cytological methods in his 

 investigations of the pineal region, gave an important description 

 of these parts from a histological point of view. d'Erchia's 

 work on Pristiurus and Torpedo has already been referred to. 

 His was the notable observation that the epiphyseal complex 

 was entirely absent in Torpedo. 



3. The pineal region in ganoids 



This region in ganoids is characterized by the presence of the 

 usual elements with the exception that the parapineal organ does 

 not develop. In A mia alone is there any rudiment of an anterior 

 portion of the epiphyseal complex, and even here it is so slight 

 as hardly to justify the attempt to homologize it with the para- 

 pineal organ in Petromyzon. Goronowitsch ('88) 153 and Kupffer 

 ('93) 223 described the pineal region in Acipenser and recognized 

 in it all of the parts usually observed in this area of the brain. 

 Following a broad lamina supraneuroporica there is a well- 

 marked paraphysis which at first is truly membranous but subse- 

 quently becomes highly vascular and takes on the form of a 

 tubular gland eventually concealing the great part of the lamina 

 terminalis. In certain forms, as in Polyodon, the paraphysis, 

 although well developed, is relatively much smaller than in 

 Acipenser. The next element in the forebrain roof, namely, 

 the velum transversum, is broad and much convoluted although 

 not very highly vascular. The dorsal sac presents the form of a 



