BY N. A. COBB. 



147 



function is the same as that of the ring in Dorylaimus, namely, to 

 serve as a guide and support to the spear. Because of its affinity 

 for carmine this threefold structure is usually conspicuous in 

 specimens treated with that reagent. That portion of the 

 oesophagus lying behind the pharyngeal bulb reminds one 

 forcibly of the corresponding part in Dorylaimus, the narrow 

 anterior half being surrounded near the middle of the neck by 

 the nerve-ring, and joined to a stouter, nearly cylindrical, 

 muscular posterior half, two-thirds as wide as the body. 



Before describing the head it is necessary to premise that the 

 cuticula is finely striated. The stria? in the single known species 

 appear like plain transverse lines '8^ apart, so that the total 

 number in the cuticula of an adult worm is calculated at about 

 twenty-seven thousand. The nearly cylindrical neck terminates 

 anteriorly in a rounded head, which bears, far forward, two large 

 and conspicuous spiral lateral organs. These commonly lie 

 opposite to, or a little in front of, the cap of the spear. The 

 striatums of the cuticula cease on the head to be transverse. One 



Fig. 4.— Lateral View of the Head of 

 Onyx perfectcs, with the mouth open 

 and displaying lips. The pharyngeal 

 bulb and its contained spear are 

 clearly shown, as is one of the spiral 

 lateral organs, and the spear-guide. 

 The left hand side of the figure is 

 dorsal, x 400. 



Fig. 5.— Lateral View of the Head of 

 Onyx perfectus, with the mouth 

 closed. The head of the spear is 

 --shown just behind the spiral lateral 

 organ. Under the cap of the spear 

 are two developing caps for future 

 use, showing neatly the manner of 

 dentition. The guides for the spear 

 are partially hidden by the spiral 

 organ. The right hand side of the 

 figure is dorsal, x 400. 



may observe them passing circularly around the lateral organs and 

 on some parts of the head they are arranged longitudinally. This 



