THE AMPHINEURA 57 
stomach is lined by a secretory, or so-called hepatic epithelium, 
and its dorsal wall is ciliated. The intestine is straight and short, 
with thin walls lined by a ciliated epithelium. The anus opens 
into the branchial or cloacal chamber, together with the kidneys 
and sometimes the anal mucous gland (Fig. 38). 
Circulatory System.—There are no true blood-vessels with 
definite walls, but there are two well-marked blood-sp 
ventral sinus between the foot and digestive tract, and a dorsal 
tubular sinus or aorta whose hinder part forms a contractile heart. 
The heart is enclosed in the pericardium and is fastened to its 
dorsal wall, except in Neomenia, where it is free. The blood is red 
owing to the presence of haemoglobin in the rounded or ovate 
blood-corpuscles. 
In the Neomeniidae and most of the Parameniidae there is a 
sa 
BIG ove 
Proneomenia gerlachet, right half of the anterior part of the body ; left-side view. 6, mouth ; 
cae, pharyngeal caecuin; com.p, pedal commissure; cu, cuticula; fo.ci, ciliated fossa ; g.c, 
cerebral ganglion ; gl.g, gonad ; gl.s, salivary gland ; gl. s.d, dorsal salivary ¢ gland ; p, foot ; pap, 
buecal papillae ; pha, pharynx ; ra, "radula : sin, ventral sinus ; st, stomach. 
more or less extensive circlet of gills on the inner walls of the 
cloacal chamber. These gills are epithelial folds or laminae, whose 
cavities communicate freely with the haemocoele and the above- 
mentioned sinuses. In the species in which no gills are present 
the venous blood of the ventral sinus is oxygenated through the 
epithelium of the inner wall of the cloacal chamber and the surface 
of the foot. Where gills are present the blood passes into them 
and is returned to the heart by two auricular ducts in Neomenia. 
Excretory Organs. — The pericardium occupies the posterior 
region of the body dorsad of the rectum. The dorsal and lateral 
parts of its inner wall are ciliated, and its cavity communicates 
with the exterior by means of a pair of renal ducts, which open 
into the cloacal chamber below the anus. In Strophomenia the renal 
orifices are adjacent, but separate from one another as in Chaetoderma, 
but in all other Neomeniomorpha the renal ducts open into the 
cloaca by a common aperture (Fig. 30, C). As in the Polyplaco- 
