NO. 2131. 



NEMATODE PARASITES OF RODENTS— HALL. 



71 



m 



pharyngeal border is an incised cuticular plate with marldngs defi- 

 nitely related to the above-mentioned lips. There is a club-shaped 

 esophagus which gradually increases in size posteriorly and finally 

 terminates in a subspherical bulb 

 which is separated by a deep con- 

 striction from the preceding por- 

 tion of the esophagus. This bulb is 

 supplied with a tripartite, chitin- 

 ized dental apparatus. The intes- 

 tine has at least one anterior and 

 one posterior local dilatation, and 

 finally terminates in a large ovoid 

 dilatation, probably having the 

 function of a colon, followed by a 

 short narrow tube to the anus. 

 There are two cervical alae, ex- 

 tending back less than half the 

 length of the esophagus. There is 

 a fine transverse striation, often 

 obscure, and the usual fine longi- 

 tudinally oblique striation due to the musculature. The nerve ring is 

 far forward on the esophagus, unusually close to the head. The 

 excretory canals unite just behind the esophageal bulb and the ex- 

 cretory pore opens 



j/iomm 



Fig. 80.— Oxyuris evoluta. Mouth viettod 

 feom the front. slightly flattened un- 

 der pressure. 



just anterior of the 

 vulva. 



Male 4.G to 6.53 

 mm. long, with a 

 maximum thick- 

 ness of about 350 [x. 

 Head diameter is 

 from 45 to 75 pi, but 

 the contour of the 

 head in this genus 

 is such that there is 

 no distinct place, as 

 a rule, at which to 

 take this measure- 

 ment. The length 

 of the esophagus, exclusive of the bulb, is 500 to 6G0 [jl and its thick- 

 ness is 70 to 105 [x. The bulb is subspherical, 145 to 175 ^ long by 135 

 to 170 [X thick. The nerve ring is 85 to 105 \i. behind the anterior end 

 of the body. The bursa is only slightly developed, but there is one pair 

 of postanal papillae which are highly developed in the form of elon- 

 gate conical rays and show a close homology with similar rays in O. 

 trlradiata which function as supporters of a well-developed bursal 



Fig. 81. — O.XYURi.s evoluta. 



Posterior extremity of male. 



LARGED. 



En- 



