576 LOCV. [Vol. XI. 



evidence is too circumstantial at present to bear the interpre- 

 tation that we already know the invertebrate homologue of the 

 vertebrate pineal organ. 



4. The Double Nature of the Epiphysis 



receives support from two sources. It is difficult to interpret 

 Klinckowstrom's discovery of a double nerve in Iguana on any 

 other hypothesis. That interpretation is also strengthened by 

 the claim I have made of tracing the epiphysis in Selachians 

 back to a pair of epithelial cups on the cephalic plate. 



Hill (-94) regards the two vesicles he has discovered in 

 Teleosts as having been primitively side by side ; and Ritter 

 ('94) has recently suggested that the epiphysis and the para- 

 pineal organ of Studnicka are right and left mates rather than 

 independent eyes of double origin. It will be remembered, in 

 this connection, that Klinckowstrom found three nerves in one 

 individual of Iguana, two from the ganglia hebenulae, and one 

 from the posterior commissure ; that Leydig discovered two 

 accessory pineal organs in Anguis ; Duval and Kalt found as 

 many as three of these organs, and I have found several pairs 

 of epithelial patches back of the eyes on the cephalic plate, and 

 have traced one pair into the epiphysis. It seems to me that 

 all this evidence is more favorable to the idea that the pineal 

 sense-organs are multiple, and individually of paired origin, than 

 to the idea expressed by Ritter. 



5. Paraphysis. 



Considerable confusion has arisen in identifying the paraph- 

 ysis in different forms. As soon as it was made known that 

 there are two outgrowths from the roof of the fore-brain, it 

 was at once assumed that the most anterior one is the paraph- 

 ysis, and the posterior one the epiphysis. But there is now 

 evidence that there are, at times, more than two outgrowths. 

 Hill has shown in Amia the presence at one and the same time 

 of three tubular outgrowths from the roof of the fore-brain. 

 Two of these come from the thalamencephalon, and the ante- 

 rior one arises from the prosencephalon. He points out that 



