THE PINEAL BODY 



87 



Studnicka 388 the parapineal organ. According to Ahlborn, 2 it 

 was the inferior vesicle of the epiphysis. Owsiannikow 295 termed 

 it the visceral vesicle, while it was called by Kupffer 222 the para- 

 physis. It presents an end-vesicle, a stalk, and a proximal 

 portion. It its general form it resembles the pineal organ and is 

 situated as a more or less distinct vesicle between the pineal 

 organ and the roof of the brain in the region immediately cephalad 

 to the habenular ganglion and the commissura habenularis. 

 The vesicular portion is in relation with the habenular ganglion, 

 being situated dorsal to it, while the stalk and proximal portion 

 are in relation with the commissura habenularis. In size the 

 parapineal organ is considerably smaller than the pineal organ, 

 and though it varies considerably in this respect, the following 

 tabulation made by Studnicka 388 shows the general dimensions 

 of the organ in Ammoccetes and Petromyzon planeri. These, 

 figures apply to the end-vesicles. 



Ahlborn 2 in 1883 found that the parapineal organ in general 

 has the same form, although it is smaller than the pineal organ 

 while the cellular elements in the two structures correspond very 

 closely. The lumen of the parapineal organ contains a fibrous 

 tissue having many histological features in common with that in 

 the pineal organ. Beard 18 in 1889 found the parapineal organ 

 in Ammocceles only a little less developed than the pineal 

 organ, in which opinion Gaskell 145 concurs. In Petromyzon 

 fluviatilis, Owsiannikow 295 in 1888 found that the parapineal 

 organ was smaller than the pineal organ, but in no other way 

 different from the latter. The end-vesicle contained a retina 



