Sorensen, Study of Epiphysis and Roof of Dienccplialon. 45 



this ridge is triangular and the median angle separates for a 

 short distance as an independent appendage. When first dis- 

 covered His thought that he had solved the history of the pin- 

 eal and only a careful profile reconstruction revealed the fact 

 that this body belonged to the very front of the roof of the 

 diencephalon and seems later to disappear in the folds of the 

 plexus. The true epiphysis, he says, develops much later, after 

 the post-commissure is already formed, by protrusion of the 

 most caudal part of the diencephalic roof. In the bird brain, 

 as even Remak noticed, the epiphysis arises from the middle of 

 the diencephalic roof and the same is true for the epiphysis 

 of reptiles. Thus we distinguish epiphyses of the front, 

 middle and posterior parts of the diencephalic roof. For the 

 latter the name pineal may be usefully retained. Besides 

 these special forms of outgrowth we encounter an elevation of 

 the whole roof as in selachians and teleosts. Gotte's "aderge- 

 flechtknoten " certainly pertains exclusively to the group of 

 anterior projections while the so-called parietal eye of reptiles 

 belongs to the middle group. 



Studnicka (££-'93) wrote an extended article on the parie- 

 tal organs of Petromyzon planeri which is here largely repro- 

 duced. His materials were : adult Petromyzon ; Ammoccetes 

 23 mm. to 140 mm. long, also some more highly developed; 

 embryonic fish eggs artificially incubated, from the stage of seg- 

 mentation up to a length of 7 mm. Embryos from 7 mm. to 

 23 mm. long and the transitional forms between Ammocoetes 

 and Petromyzon were not available. In his preparations Stud- 

 nicka used chromic acid or sublimate for the embryos. For 

 Ammoccetes and the adult Petromyzon good results were 

 secured with y z per cent, chromic acid ; Miiller's fluid and sub- 

 limate were used in some cases. Nitric acid (4 per cent.) was 

 found to be of little value. 



A. Embryology and Anatomy. 



The pineal organ of Petromyzon is a simple evagination of 

 the diencephalon behind the supra-commissure. Describing the 

 evagination the author says in substance : At first this simple 



