370 JOHN WARREN 



11. The superior commissure is well developed in both lizard 

 and turtle. It appears in the former in embryos of about 17 mm. 

 and in the latter in embryos of about 8.9 ram. In both cases it 

 is coincident with the first appearance of the anlage of the lateral 

 plexuses. 



12. The posterior commissure develops first in the roof of the 

 synencephalon or second subdivision of the diencephalon. It in- 

 vades the mid brain later. 



13. The plexus choroideus lateralis is much better developed 

 in the turtle than in the lizard. It appears in the former in 

 embryos of about 8.9 mm., in the latter in embryos of about 17 

 mm. 



The diencephalic plexus is very much more highly developed 

 in the turtle than in the lizard. It forms two lateral masses that 

 occupy the whole length of the dorsal sack from the velum to the 

 supra commissure. Its anlagen appear first in embryos of about 

 16 mm. In the lizard it appears later, 37 mm., and occupies the 

 apex only of the narrow dorsal sack. 



The telencephalic plexus or plexus inferioris in the turtle is 

 possibly represented by short bilateral prolongations growing 

 caudad from the lateral plexus. There is no sign of them in the 

 lizard. 



In conclusion I wish to acknowledge the valuable advice and 

 assistance kindly given me by Professor Minot in the preparation 

 of this article. 



ADDENDA 



I regret that I was unable to consult the two following papers 

 before the main part of my article was written and sent in for 

 publication. The first paper by Tandler and Kantor (105) 

 gives a most admirable series of pictures of models of the brain 

 of the gecko. The general development of the pineal region 

 corresponds closely to that shown in my models. The para- 

 physis, however, is carried backward until its tip overlaps the 

 epiphysis and both of these structures are crowded against the 

 wall of the mid brain. In the oldest stage (fig. 17) there is no 

 diencephalic choroid plexus in the dorsal sack and no signs at 

 any stage of the pineal eye. The synencephalic segment of the 



