THE PINEAL ORGAN 



beneath the larger. In this position, where it lies under cover of the 

 superficial vesicle, it is obvious that the smaller, less differentiated organ 

 has become quite functionless as a visual organ and that the small size 



Par PI 



R.Pm.N. 



N.Ch 



Ch.PI. — m^# 



gf^Pigm.C. 



#--R.ParO 



Sg»fr — L.Par.O. 



\ _vw|^L — L.Pin.N. 



_A_. ^4__LHab.G. 



am-R.Hab.G. 



/~~ W amJerm 



^Opt Ch. 



R.F. Cbl. Hyp. 



Fig. 134. — Sagittal Section through the Head of the New Zealand Lamprey 

 (Geotria), showing the General Position and Connections of the Right 

 and Left Pineal Eyes. (After Dendy.) 



Aq. C. : aqueductus cerebri. 



Cbl. : cerebellum. 



Ch. PL : choroid plexus. 



Cr. C. : cranial capsule. 



Ep. : epidermis. 



Hyp. : hypophysis. 



Lam. Term. : lamina terminalis. 



L. Hab. G. : left habenular ganglion. 



L. Par. O. : left parietal organ (parapineal organ). 



L. Pin. N. : left pineal nerve. 



Muse. : muscle. 



N. Ch. : notochord. 



Opt. Ch. : optic chiasma. 



Par. PL : parietal plug. 



Pigm. C. : pigment cells. 



Post Com. : posterior commissure. 



R.F. : Reissner's fibre. 



R. Hab. G. : right habenular ganglion. 



R. Par. O. : right parietal organ. 



IV. Ve. : fourth ventricle. 



of the left habenular ganglion as compared with the right, is correlated 

 with this displacement and loss of function. Lying directly over the 

 larger vesicle, is a thick conical plug of translucent mesenchymatous 



