436 



mid and hind brains of the Trout and Salamander at least S segments 

 and, if I understand him correctly, says, these segments not only cor- 

 respond to the lateral somites (p. 476 but that there is something 

 similar to these brain segments to be observed in the spinal cord. He 

 concludes however by expressing the opinion (p. 477), that the fore 

 brain is not to be reckoned in the segmental region. He does not, in 

 this brief paper, give any of the histological characteristics of the seg- 

 ments. I am indei)ted to this paper for many bibliographical references. 

 Gegenbau r^ has recently expressed the following opinion: 'So 

 interessant und so vielversprechend diese Thatsachen sind, so wenig 

 scheinen sie mir gegenwärtig geeignet, zur Beurtheilung der Metamerie 

 des Kopfes selbst als Factoren in Geltung gebracht zu werden. Das 

 wird erst eintreten können, wenn ihre Beziehung zu anderen, den 

 Kopf aufbauenden Organen erkannt ist.' In lbb7, Orr^'^ described 

 6 folds in the hind brain of the Lizard, 5 of which of equal size and 

 the G^^, from which the 10^^ nerve originates, somewhat longer than 

 the others. He described the mid brain as consisting of one fold and 

 in addition to this described two folds in the primitive fore 

 brain. He gave the name »neuromeresi to these folds, a name pre- 

 viously used with a somewhat diiferent significance by Ahi borni'. 

 Orr found that the V, VII, YHI, IX and X nerves each originated in 

 connection with a neuromere which degenerated after the nerve was 

 formed. He fully described the structure of a Jiieuromere t, which I 

 quote, as it bears directly on my own work. 



1) »Each neuromere is separated from its neighbors by an externo- 

 dorso -ventral constriction, and opposite to this an interno -ventral 

 ridge, — so that each neuromere i. e., one lateral half of each), 

 appears as a small arc of a circle.« 



j)The constrictions are exactly alike on each side of the brain, f 



2) «The elongated cells are placed radially to the inner curved 

 surface of the neuromere.« 



3) )^The nuclei are generally nearer the outer surface and approach 

 the inner surface only towards the apex of the ridge.« 



4 ))0n the line between the apex of the internal ridge and the pit 

 of the external depression, the cells of adjoining neuromeres are 



^ Die Metamerie des Kopfes und die AVirbeltheorie des Kopfskelettes. Morph. 

 Jahrb. 13. Bd. p. 37. 



>o A Contribution to the Embryolog}- of the Lizard. Journ. of Morphol. Vol. I. 

 No. 2. Dee. 18S7. 



n Über die Segmentation des Wirbelthierkörpers. Göttingen, 4. Januar 1S84, 

 p. 312. 



