170 W. BALDWIN SPENOEE. 



terminal division of the left ganglion habenulse, whereby is 

 simulated the existence of a primitive genetic connection of the 

 epiphysis with the anterior roof of the thalamencephalon. 



In the epiphysis Ahlborn states that three parts can be dis- 

 tinguished clearly separated off from each other. 



(1) A hinder thread-like stalk. 



(2) Two anterior vesicles lying upon one another (Taf. xiii, 

 fig. 2, and Taf. xvi, figs. 43, 44, 46, and 47). The latter form, 

 the " Weisse kuchenartige Masse," which Wiedersheim recog- 

 nised as the primitive pineal gland, and lie above the point of 

 the beak-shaped roof of the thalamencephalon. The thread- 

 like stalk is attached to the upper vesicle, and corresponds to 

 the proximal and median part of the epiphysis of Selachians 

 and Amphibians (and we may now add to the stalk connecting 

 the " eye" with the dorsal surface of the thalamencephalon of 

 Lacertilia) . 



The distal portion of the epiphysis consists of two vesicles, of 

 which the upper is the larger ; their cavities, save in rare cases, 

 do not communicate with each other. Ahlborn describes the 

 upper vesicle as being a delicate hollow structure, flattened 

 out dorso-ventrally, and placed close to the skeletogenous roof 

 of the cranial cavity. The cells of the lower wall are always 

 much thicker and deeper than those of the upper, and in his 

 figures (Taf. xvi, figs. 44, 46, and 47), though he does not 

 describe them minutely, are seen to have their long rod-like 

 ends free from nuclei, and turned towards the cavity, whilst the 

 nuclei are all placed close to their external extremities. These 

 rod-like structures, however, are quite devoid of pigment, and, 

 moreover, have a thin but well-marked layer of nervous matter 

 present between them and the cavity of the vesicle, which is 

 itself apparently occupied by strands of nervous tissue passing 

 from the posterior to the thin anterior wall. There is nothing 

 comparable to a lens. 



The under vesicle is attached on its ventral surface to the 

 left ganglion habenulae (the whole organ is placed asymmetri- 

 cally, and lies on the left side), whilst its upper wall is fused 

 with the larger upper vesicle. This secondary fusion with 



