152 Journal of Comparative Neurology. 



it does not conform to true (mesomeric) segmentation. 

 Neuromerism is secondary — conditioned by mesomerism. 



Froriep found special dorsal branches of the hypoglossus 

 and considers this nerve distinct from the vagus and composed 

 of several cranial nerves while the vagus is a complex of seg- 

 mental cranial nerves. The occipital region should be mor- 

 phologically mcluded with the spinal cord. Froriep also 

 announced that ganglia on the facial, glosso-pharyngeal and 

 vagus are connected with the skin. ^■ 



These points are anlags of sensory organs analogous with 

 the organs of the lateral line, but never attain functional devel- 

 opment. Baird's paper on the same subject was adequately re- 

 reviewed in the paper above referred to, in volume I. The 

 views of VVeidersheim are similar to those of Baird and are ex- 

 pressed in the familiar diagram in his Comparative Anatomy. 



Gegenbaur, in his paper entitled " Ueber die Metamerie 

 des Kopfes und die Wirbeltheorie des Kopfskelettes," enters 

 into an extensive criticism of previous authors. He considers 

 Van Wijhe's head somites very dissimilar structures containing 

 elements from the trunk. He does not accept the double na- 

 ture of the hyoid arch. The 4th, 5th, and 6th segments are 

 rudimentary. The 7th, 8th, and 9th are trunk segments. Ge- 

 genbaur does not accept the identification of the lense capsule, 

 hypophysis, auditory vesicle, spiracle, etc., with gill clefts. He 

 thmks there was originally complete concordance between 

 branchiomerism and mesomerism, but that subsequently, by a dis- 

 appearance of some branchial arches trunk segments are pro- 

 jected forward. Olfactories and optic are not included among 

 segmental nerves. Admitting the possibility that the oculomo- 

 tor may belong to Van Wijhe's first segment with the R. opthal- 

 amicus as dorsal root,' he considers the first real metamer the 

 second segment of Van Wijhe with the first gill arch. The 

 trochlearis belongs to the former and the R. mandibularis trig, 

 to the latter. The second metamer consists dorsally of the third 

 and part of the fourth somite and ventrally of the second gill 

 arch and has the abducens and acusticofacial nerves. 



I. Refer to paper by Prof. Kupffer in vol. I., October and Decem- 

 ber, 1891. 



