286 S?isd?i?ia Phelps Gage 



Since the researches of Ahlborn (i) showed the nature 

 of the pineal eye or epiphysis in lamprey, it has been settled 

 that its stalk retains its connection with the brain at least 

 through larval life. This connection is very clear in the spec- 

 imens studied (Fig. 103), but the nerve which Beraneck (5) 

 claims to have found connecting the epiphysis to the mesen- 

 encephal, was not seen. The pigment of the organ agrees 

 with the condition said to belong to this stage of develop- 

 ment by Beard (4), that is, it is white by reflected light. He 

 says that in both earlier and later stages black pigment is 

 found. The white pigment extends from the floor of the 

 epiphysis into the hollow stalk for some little distance (Fig. 

 104, 105) then the stalk becomes inconspicuous and passes be- 

 tween the two habenas, to its union with the brain at the left 

 of the middle, but on a 7norphological meson (Fig. 103, 109). 



Paraphysis. — In diemyctylus before hatching, a cross parti- 

 tion divides the prosen- from the diencephal and from this is 

 another dividing the prosencephal into right and left hemicere- 

 brums. This T shaped partition so formed is permanent. 

 Into the space where the two bars join is developed from the 

 brain cavity the first trace of the paraph3'sis (Fig. 73). This, 

 from the curvature of the brain, is a cephalic structure. 

 When the flexure is lost the paraphysis retains its relative po- 

 sition but becomes a dorsal .structure (Fig. 67), the stem of the 

 T is represented by the mesal walls of the hemicerebrums with 

 intervening pia, the cross bar is the fold cephalad of the di- 

 encephal in which the supraplexus and paraphysis occur. In 

 the larva the tube has an enlarged bulbous end (Fig. 66) and 

 is composed of a single layer of cubical epithelium. Around 

 this tube are a few small vessels and scattered cells, the begin- 

 nings of the supraplexus. Eycleshymer (12) identified and 

 has given an excellent account of the paraphysis in amblys- 

 toma up to this point of development, but in 14 mm. larvae 

 he says its proximal cavity is obliterated. This is not the 

 case in diemyctylus, for in the adult the connection with the 

 brain cavity still exists though it is con.stricted. The cavity 

 continues to increase in size but by the beginning red stage 

 it is convoluted by the growth of blood vessels which press 



