244 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
formation of the three brain vesicles, and long after the segmentation of 
the mesoderm ” ! 
McClure (89, p. 435, ànd ’90, p. 37) concluded, from studies on em- 
bryos of Amblystoma, Anolis, and chick, “that the symmetrical con- 
strictions or folds foynd in the lateral walls of the embryonic brain are 
remains of the primitive segmentation of the neural tube, in part atavis- 
tic, extending [from the spinal cord region] into the primary forebrain.” 
The serial homology of the segments of the myelon and the encephalon 
seemed to him certain, since he found both the structural characteristics 
and the nerve relations to be the same in the two regions. “ The dorsal 
roots of spinal nerves take their origin from the apex of their respective 
myelomeres in exactly the same manner as the nerves of the medulla 
do from their respective encephalomeres ” (89, p. 437). 
In the same year Miss Platt (’89) also advocated the view that there 
is a serial homology between the encephalomeres and the segments of 
the spinal cord. While she agrees with Orr and Béraneck in regard to 
the number and appearance of the neuromeres and the ultimate rela- 
tions of the nerves, she finds that the cranial nerves develop from the 
constrictions between neuromeres, precisely as the spinal nerves do. In 
answer to objections to the attempted homology between cranial and 
spinal segments, she says that in both head and trunk the segmentation 
is transitory, and that in both regions it ig more manifest in the ventral 
portion of the neural tube. 
The conclusions of Waters ('91) are largely confirmatory of those of 
McClure, viz. that ther® is a similar segmentation in brain and spinal 
cord, with similar sensor nerve relations in both these regions. 
Zimmermann (’91), as a result of his studies on rabbit, chick, and 
Squalus embryos, thinks he is able to confirm Kupffer’s discovery of 
eight primary cephalic segments or “ encephalomeres,” although his 
eight “ primäre Abschnitte” include forebrain, midbrain, and hindbrain 
regions, while Kupffer’s theoretical conclusion was that his eight “ pri- 
mire Medullarfalten ” do not include the hindbrain.! Although Zim- 
mermann states that the spinal cord does not appear segmented, he 
finds in later stages thirteen homodynamous “ encephalomeres,” and has 
given a table of these with their nerve relations. He supposes three 
roots, a dorsal, a lateral, and a ventral one, to be related to each en- 
cephalomere, but his table gives chiefly the impression of numerous gaps 
to be filled with hypothetical nerve roots. 
Herrick (92) states that he finds the segmentation of the medulla 
1 At first Kupffer thought they did not include the forebrain ! 
