334 JouRNAL OF COMPARATIVE NEUROLOGY. 
posteriorly (caudad) from the ganglion cell and terminates in 
the next ganglion; D, where the fiber passes anteriorly (cephal- 
ad) from the ganglion cell, giving off branches to the next gan- 
glion and terminating in the next but one. A may either 
decussate or not decussate, B decussates, but C and D never 
decussate. 
Class 2, which is composed of motor elements, is com- 
posed of seven classes: E, fiber enters the lateral anterior root 
of the same side; F, fiber branches and enters the same root 
from a ventral cell; G, cell situated in the median mass, the 
fiber enters the anterior root without branching; H, cell lies 
in the median mass, the fiber branches, then enters the anterior 
root; I, cell is situated in the median mass, the fiber branches 
and enters the posterior root; K, cell is situated in the median 
mass, the fiber decussates and enters the posterior root; L, cell 
lies near the median mass, the fiber enters the anterior root. 
The elements of class 3 are sensory. On entering the gan- 
glion each fiber split forming a Y, one branch of which passes 
forward (cephalad) and the other backwards. 
Since frequent comparisons will be made with the annelid 
brain, it is thought wise to give the following few résumés. 
Epwin S. Goopricu (’97) in comparing the Arthropod 
and Annelid head reached the following conclusions : 
The prostomium may be one of three things: (1) a modi- 
fied or reduced segment, (2) an incipient segment growing on 
the anterior surface of the peristomium, (3) not a segment at all 
but a peculiar structure. 
In the development of Arthropods, new segments are in- 
variably added between the last segment, the telson, and the 
one immediately in front of it. All apparent exceptions to this 
law of Mitne-Epwarps seem to®be due to retardation of de- 
velopment. 
Careful modern researches show that in the Ofgochetes 
the peristomium exhibits the essential characters of a true seg- 
ment. It is developed around the mouth and contains: (1) a 
mesoblastic somite, which becomes hollowed out to form a 
ccelom ; (2) a pair of ventral ganglia, which fuse with the suc- 
Oy a ee 
