NATURAL HISTORY OF THE BAY SCALLOP 
593 
(See fig. 14.) The lateral pallial nerves which arise under the lateral lobes, that is, 
between the ganglia and the adductor muscle, pass principally ventral of the kidneys 
along the sheath of the adductor muscle and (on the right side) the support of the 
branchial axis to the mantle and spread through it (fig. 13) to the circumpallial 
nerves. Posterio-ventrally to the lateral, arise the posterior pallial nerves which 
join with the circumpallial nerve near the 
posterior end of the hinge. Each of the 
two branchial nerves has a double origin. 
One of these lies under the lateral lobe, 
anterio-dorsal of the lateral pallial nerves, 
the other on the surface of the central 
portion of the ganglionic mass between a 
lateral lobe and the central lobe. These 
roots of the branchial nerves are cross con- 
nected near the base. They pass along the 
ventro-lateral edges of the kidneys and 
thence to the branchial axes and along 
them to the tips. For a more detailed 
study of the visceral ganglion and the 
nerves arising therein see Dakin (1910). 
Where a cerebro-visceral connective 
joins the visceral ganglion there arises, on 
each side, a small body which corresponds 
to the “swelling” of Drew (1906) and the 
accessory ganglion of Dakin (1910). Each 
of these bodies is connected with the 
branchial nerve near its base and at the 
tip gives off three branches. One of these 
parallels for a considerable distance a 
cerebro-visceral connective. Another, 
developing several obvious branches, ex- 
tends somewhat dorsallyl toward the 
anterio-ventral surface of the visceral 
mass. The third extends into the overly- 
ing tissue of the visceral mass (ovary, 
etc.), and, according not only to several 
dissections but also to observation of 
material cleared in glycerin, joins its fellow 
from the other side. (Fig. 14.) Thus 
these bodies or accessory ganglia supply 
various portions of the visceral mass and 
are interconnected through a structure 
apparently not heretofore observed. 
The abdominal sense organ (Dakin, 1909 and 1910) is to be found on the edge 
of a connective-tissue flap near the right pallial lobe. It is small, elongate, somewhat 
brownish, and covered with a dense mat of fibers. Dakin (1910) was unable to find 
any effect made by its removal or “stimulation.” Without supporting evidence, 
various functions, such as water testing and detection of movements in the water, 
have been attributed to it. 
Figure 14. — Central nervous system. Ac. G., Accessory 
ganglion; A. P., anterior pallial nerve; Br., branchial 
nerve; C. Com., cerebral commissure; C. G., cerebral 
ganglion; C-P. C., cerebro-pedal connective; C-V. C., 
cerebro-visceral connective; L., nerve to tufted lips; 
L. P., lateral pallial nerves; Os. Br., osphradio-branchial 
nerve; Of., otocyst; Of. C., otocystic canal; Of. N., oto- 
cystic nerve; Pa., palpal nerve; Pe., pedal nerve; P. G., 
pedal ganglion; P. P., posterior pallial nerve; V., nerve 
of the visceral mass; V. G., visceral ganglion (with cres- 
centric “lateral lobes” and central portion with large 
globular “ventro-central lobe” and paired “ dorso-central 
lobes”); and X., structure of unknown designation 
