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-spaces a 

 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 



I'roneomenia gerhicliei, right half of the anterior part of the body ; left-side view, ft, mouth ; 

 cae, pharyngeal caecum ; com.p, pedal commissure ; cu, cuticula ; fo.ci, ciliated fossa ; $.c, 

 cerebral ganglion ; gl.tj, gonad ; gl.s, salivary gland ; gl.s.d, dorsal salivary gland ; />, foot ; pap, 

 buccal 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- 



