| 
108 Comparative Neurology. (February, 
6. Brachiopoda —Degraded secondary. 
Resemble Vermes. 
7, Mollusca. Secondary feeble in Lamellibranchiata. 
Secondary well formed in Gastropoda. 
Secondary well defined (extending by 
commissures dorsally (?) Copelata). 
8. Tunicata. First appearance of extended secondary 
in Invertebrata. 
L Anterior ganglia vesicularly developed. 
Gegenbaur (p. 501) justifies this view of the central nervous 
system of Vertebrata being homologous with the superior central 
ganglia of Invertebrata “in an exceedingly high state of develop- 
ment.” 
The dorsal position of the central nervous system can be well 
made out in Tunicata. It proceeds from ectodermal differen- 
tiation. 
An anterior larger mass divides into three consecutive (sec- 
- ondary) lobes, produced by unequal thickening of the walls of the 
central tube. 
The anterior mass is in connection with the origin of the visual 
organs in Ascidiz, Salpze and Copelata. 
A median dorsal nerve cord appears in ascidian larvae, which 
prolongation Gegenbaur, p. 396, regards as noteworthy as being 
the only dorsal prolongation in Invertebrata, and thus a medullary 
secondary central system appears stretching the length of the 
animal. 
Notwithstanding the feeble development of the cerebral ganglia 
in Mollusca, the homology of these ganglia with the cerebral 
ganglia of Vermes and of Arthropoda has been clearly made out. 
There exist in Arthropoda and Mollusca cerebral (secondary) 
ganglia connected with nerves of special sense and visceral (pri- 
mary) ganglia innervating, in Mollusca, the heart, branchial appa- 
ratus and generative organs, comparable to the “ stomato gastric 
nervous system” of Arthropoda. — ) 
The ventral chain of ganglia, so obvious in Crustacea and In- 
secta, partakes of primary -or secondary characteristics, or both, 
depending upon the position of the metamera and the degree of 
development they have undergone. With concrescence of the 
anterior metamera into a more or less extended cephalothorax, 
the anterior ganglionic masses are fused, as in Stomapoda, where 
