THE SCAPHOPODA 201 
admit of the expulsion of blood during violent contractions of the 
body (Fig. 182, 0). There is no specialised respiratory apparatus. 
Respiration is effected by the internal surface of the mantle, 
particularly by the anterior ventral region. 
3. Hacretory Organs.—The Scaphopoda have two symmetrical 
kidneys, situated in front of the gonad on the ventral side of the 
middle of the body (Figs. 181, g, and 182, %). They have the form 
of two short but fairly wide sacs with pleated walls, lying between 
the intestinal mass and the stomach. They have no communica- 
tion with one another and have no reno-pericardial duct. They 
open to the exterior on either side of the anus. 
4. Nervous System and Sense Organs.—The nervous system of the 
Scaphopoda comprises the same four pairs of principal nerve ganglia 
as are found in the Gastropoda and Lamellibranchia, in addition to 
the stomato-gastric system. The cerebral ganglia are joined to one 
another and are situated on the dorsal side of the oesophagus: they 
innervate the proboscis with its palps and the tentacular lobes and 
captacula. Each cerebral ganglion is in close juxtaposition to the 
corresponding pleural ganglion (Fig. 182, ¢.g, pl.g), which innervates 
the mantle. The cerebral and pleural ganglia are united to the 
pedal ganglion of the same side by a long connective which is 
apparently single in the distal part of its course, but bifurcates just 
before it reaches the cerebral and pleural ganglia, sending a branch 
to each. The two pedal ganglia are situated in the foot (Fig. 
182, p.g) and are attached to one another. 
The visceral commissure takes its origin from the pleural ganglia. 
It is rather long, and bears on the posterior part of its course two 
symmetrical visceral centres (Fig. 182, v.g) in the form of simple and 
ill-defined ganglionic swellings, lying on either side of the anus close 
beneath the tegumentary epithelium, and thus resembling the 
visceral ganglia of the Lamellibranchia. These two centres are 
united by a commissure passing in front of the rectum. 
From the cerebral ganglia there arises—as in many other 
Molluscs—an infra-oesophageal labial commissure (Fig. 182, /a.c), 
bearing a ganglion on either side, from which a branch of the stomato- 
gastric commissure properly so called (Fig. 182, sf.) is given off, as 
is the case in the Polyplacophora, Aspidobranchia, and Cephalopoda. 
The stomato-gastric commissure passes to the ventral side of the 
oesophagus, between it and the buccal bulb, and bears two or four 
symmetrical ganglia on the middle of its course. The labial com- 
missure also gives off a nerve on each side, which passes to the 
subradular organ and terminates below it in a ganglion. 
The Scaphopoda have only three differentiated sensory organs : 
the captacula or tentacular filaments, the subradular organ, and the 
otocysts. The tentacles, which are seemingly tactile and olfactory 
organs, are dorsal in position and have the form of flattened lobes 
