588 THE AMERICAN NATURALIST. [Vou. XXXII. 
coast. Only a few categorical statements can be made here concern- 
ing his conclusions. The work was begun to ascertain in how far 
the neuromeres of Locy could be used in solving the problem of the 
number of segments in the vertebrate head. His conclusions on 
this point are that these structures are not of segmental value ; that 
in no case are they symmetrical on the two sides of the embryo, and 
no definite relations to the somites could be ascertained. Again, he 
has been unable to trace these dorsal structures into the hind-brain 
neuromeres. Neal regards them, and this opinion seems plausible 
to the reviewer, as results of unequal growth along the margin of the 
ventral plate. He differs, too, from Locy in his determination of the 
posterior limits of the expanded cephalic plate, the posterior boun- 
dary of which corresponds to the hinder margin of the later auditory 
invagination. 
Next Dr. Neal considers the neuromeres of Orr. In the hind- 
brain region he accepts these structures as metameric in character, 
but points out that Orr’s criteria apply only to the later stages ; in 
earlier embryos the constrictions separating the neuromeres are not 
only lateral, but dorsal and ventral as well. These neuromeres are 
entirely independent of influence from the mesoderm, and as paired 
ganglionic enlargements of the central nervous system at once sug- 
gest comparisons with the ventral cord of annelids. In the region 
of the spinal cord, on the other hand, the neuromeres differ some- 
what in structure and development from those of the hind-brain, and 
their existence, at least in part, seems to depend upon the adjacent 
segments of the epimere. 
The so-called neuromeres of the fore- and mid-brain regions are 
not equal to those of the other part of the brain, as they are later in 
appearance and are ccenogenetic in character. The two primary 
vesicles, fore-brain and mid-brain, are each of neuromeric value. 
So, counting all these, Neal recognizes one each for the fore- and 
mid-brains, and five in the hind-brain back to the “ Urvagus,” a total 
of seven in the primitive head. He fails to see marked differences 
between the pre- and post-auditory regions of the head, and regards 
the somites as serially homologous. 
The relations of the neuromeres to other apparently segmental 
structures is then taken up with the following results, the table being 
slightly altered in its arrangement from that of Neal : 
