340 : The American Naturalist. [Apa 
Hoffmann found that the trochlear nerve arises in the lizard from is 
the anterior neuromere of the hindbrain, and subsequently shifts _ : 
forward to the midbrain. McClure promises to prove that Hof. 
man has probably mistaken the posterior segment of the mid- — 
brain for the anterior segment of the hindbrain, but as he figures 
in the chick and lizard an unnamed neuromere between the mid- 
brain and trigeminal neuromere, the promise is not fulfilled r 
This ungamed neuromere is described by Orr. Hoffman says it — 
forms part of the cerebellum. Miss Platt, with whom McClure 
closely agrees in many points, but whose work he utterly ignores, 
states essentially the same. Four neuromeres of the hindbrain 
give rise to dorsal nerve-roots. The abducens and auditory 
neuromeres possess no nerve-roots, and in Amblystoma the 
abducens neuromere is wanting. -The VI. nerve cannot be cer- 
tainly identified with any neuromere. It should be noticed that 
while McClure gives theoretical evidence for the separate origin 
of the VII. and VIII. nerves, Miss Platt has already demonstrated 
the same. McClure agrees with Miss Platt in homologizing the 
neuromeres of the brain with those of the spinal cord. He con- 
siders the dorsal roots of the nerves to arise from the outward 
convexity of the respective ‘neuromeres, or to be intersomitic. 
Miss Platt says that in the chick the spinal nerves spring from 
the internal ridge opposite the myotomes or somites. Houssay 
says that in the Axolotl the dorsal nerve-roots arise each | ir € 
the neurotome of its segment. “Nine myotomes in the bo 
region would correspond to the nine spaces between ten net 
meres of the spinal cord. Therefore our author says the ) ‘ 
mesodermal head-somites, or myotomes, of Van Wijhe “the 
retically correspond to the nine spaces between the ten enc 
alomeres.” 7 
Ayers (’90a,’908) sees in Amphioxus, which, as Steiner she 
consists of a series of physiologically equal segments, 2 | 
comparable to the brain of higher vertebrates. The anem 
of the neural axis of Amphioxus is a brain, for it termina 
head. Moreover, Dohrn’s recent investigations show conclusively hat 
brain consisted of many more than ten segments. ; 
1 This statement shows a surprising lack of acquaintance with the morp er 
