570 LOCY. [Vol. XI. 



In this specimen the paraphysis had made its appearance as 

 an outgrowth from the cerebrum. It is relatively late in aris- 

 ing, and is entirely distinct from any outgrowth from the 

 thalamencephalon. The lateral walls of the mid-brain are no 

 longer lobed as in earlier stages. Fig. 58 is the same brain 

 viewed from above ; we are looking directly into the cavity of 

 the fourth ventricle. 



Fig. 60 shows the brain of a still older embryo. It is the 

 largest embryo of Squalus in my collection, measuring 35 mm. 

 in length. The cerebral lobes are divided into right and left 

 halves by a shallow furrow. From the back of the cerebrum 

 rises the paraphysis {p)\ just behind this is seen the semi- 

 circular fold, belonging to the 'tween-brain, and behind that is 

 the epiphysis, rising above and resting upon the anterior wall 

 of the mid-brain. Fig. 61 shows a front view of the cerebral 

 lobes after being removed from the rest of the brain ; the 

 paraphysis is also brought into view. Fig. 62 is the same 

 brain with the cerebral lobes removed, and placed so as to give 

 a full-face view on the epiphysis ; the stalk is considerably 

 longer than in Fig. 59. 



I have not had material to work out the subsequent history 

 of the epiphysis. In specimens about six inches long it is situ- 

 ated in the wall of the cranium, directly over the cerebral lobes, 

 and is connected to the roof of the 'tween-brain by a long 

 thread-like stalk. The enlarged distal end is about the same 

 size as in Fig. 62. Cattie shows it in the adult with several 

 capsules on the end of the stalk. 



Sections of the stages just studied serve to confirm the 

 observations made from the outside. They do not add very 

 much to its features, speaking strictly morphologically. The 

 surface views have been prepared in such a way that they may 

 stand for reconstruction, but they are more accurate than any 

 actual reconstruction can be, as they show the relations entirely 

 undisturbed. 



Figs. 1 19-124 show a series of sagittal sections covering the 

 period of the first appearance of the epiphysis, the reduction of 

 the anterior part of the thalamencephalon, and the beginning of 

 the paraphysis and the choroid plexus. 



