476 Leland Griggs. 



half of it comprises the infundibulum or infundibular depression 

 and the base of the eye stalk. Between the parencephalon and 

 the mid-brain is a small wedge-shaped region, the synencephalon, 

 a region which in fish embryos is prominent but whiph is hardlj^ 

 noticeable in Amblystoma. The temporary appearance in the 

 mid-brain of two swellings is, according to Kupffer, almost uni- 

 versal among vertebrates. It has been found in various types 

 by Locy, Hill and Johnston. It is undoubtedly present for a 

 short time in the optic lobes of Amblystoma but it soon disappears 

 and the mid-brain becomes an unsegmented region with a narrow 

 ventricle and thick walls as shown in the older embryo seen 

 in fig. 12, D. In the hind brain the most important swelling 

 has been called the cerebellar crest. As first described it lies 

 directly behind the mid-brain but in older stages it migrates 

 slightly backward leaving a triangular region in which the adult 

 cerebellum arises. This triangular region is called by most 

 authors a distinct cerebellar neuromere. Amblystoma, and 

 according to McClure ('90) Kupffer ('05) and Johnston ('05) 

 all the Amphibia as well, lack the so called "blank neuromere" 

 which is found in the embryos of many vertebrates just behind 

 the swelling described above. The second swelling in the hind- 

 brain of Amblystoma resembles the first. Behind the otic pit 

 lies a third swelling resembling the first two. These swellings 

 of the hind-brain may well be called true neuromeres since as 

 Johnston and Locy have shown they are like the undoubted 

 segments of the spinal cord, and since there are no accessory 

 structures behind the cerebellum to produce secondary divis- 

 ions. 



There are then in the closed neural tube of Amblystoma a 

 series of swellings extending from the anterior end of the brain 

 to the otic pit, but since these divisions are of varying morpho- 

 logical significance they cannot rightly be called neuromeres. 

 If no such general term is applied to them as a group considerable 

 confusion may be avoided, for then the morphology of each may 

 be investigated on its own merits as it has been the aim of this 

 paper to do. 



