104 Proceedings of the Royal Society of Victoria. 



The brain of the specimen examined hj myself was not, 

 unfortunately^ in a good state of preservation, not having 

 been intended especially for histological work. Externally 

 there was when preserved in spirit no indication of the 

 presence of a Pineal eye. In a specimen of Petromyzon 

 which has lain for some time in turpentine so as to render 

 the tissues somewhat transparent, there is a strongly 

 marked white spot indicating the epiphysis lying beneath, 

 but in Mordacia no such indication was visible. 



Longitudinal vertical sections, however, revealed the fact 

 that the larger vesicle is attached by a stalk to the dorsal 

 surface of the brain, and that in its walls an abundant 

 deposit of pigment of a dark brown colour is developed. 



The vesicle is of large size, and is flattened out against 

 the roof of the brain case, and it maj- perhaps be due to the 

 state of preservation of the brain in the particular specimen 

 examined, but I could find no trace of the lower of the two 

 vesicles normally present in Cyclostomata. 



The eye stretches forward much compressed dorso- 

 ventrally, and overlaps tlie cerebral hemispheres, its 

 jiosterior end being continuous with the optic stalk, and 

 being somewhat swollen out. Its walls are composed 

 of long rod-like cells embedded in brown pigment, and 

 facing into the cavity of the vesicle. These cells are longest 

 at the posterior end, where the stalk joins the vesicle, 

 i-esembliiig thus the eye in many Lacertilia, and the whole 

 structure is very similar to that figured l)y Beard as present 

 in Petromyzon* The rod- cells appear to be in connection 

 at their outer ends with nuclei, though these could not ]:)e 

 detected with absolute certainty, owing to the incomplete 

 liistological state of the brain. My experience of other 

 Pineal eyes makes me have little doubt, however, that they 

 are present. 



Of a true lens, that is of a cellular structure which could 

 serve to focus rays of light entering the eye, it must be 

 confessed, that neither here nor in the specimens figured by 

 Beard, can one be said to be present. The vesicle wall is 

 complete, and anteriorly consists simply of a comparatively 

 thin layer, in which no pigment is deposited, and through 

 which rays could easily pass to impinge upon the retina 

 beneath. The layer appears to be of equal thickness all the 

 way across, and there is no median swelling out, such as is 



* Op. cit. PI. VI., Fig. 1. 



