MICROMICRON, MESODORUS 325 



body. Just behind the base of the neck, there are cells which stain a little more 

 strongly than the adjacent structures, possibly renette cells. The tail of the 

 male is conoid to the terminus, where it has a width one-fourth as great as at 

 its base. The caudal glands seem to be located in the base-of the tail. The pres- 

 ence of a series of ventral supplementary organs is indicated by corrugations 

 occurring in the cuticle on the ventral surface when the posterior extremity is 

 incurved. This series extends from the anus forward a distance about equal 

 to twice the length of the tail, and must be composed of about 

 twenty elements. Each probably consists of an inconspicuous 

 modification of the ordinary cuticle, in the midst of which there 

 is a nerve ending. In front of the anus on the ventrally sub- 

 median lines there are series of setae, each seta being nearly one- 

 third as long as the body is wide. There is one of these setae 

 in front of the anus on each side, a second pair nearly opposite 

 the proximal ends of the spicula, and so on. Similar setae occur on the anterior 

 two-thirds of the tail on the submedian lines. When seen in profile, the spicula 

 appear at the middle to be about one-third as wide as the body. They taper 

 rapidly to the acute distal extremities. The proximal ends are slightly arcuate 

 in a ventral direction. Near the proximal extremities there is a break in the 

 framework on the ventral side. The framework of the spicula is rather frail, 

 considering the size of the spicula themselves. Muscular fibers appear to pass 

 from the inner free end of the accessory piece backward to the ventral surface 

 of the anterior portion of the tail. 



Habitat: Punta Arenas, Pacific Coast of Costa Rica. The intestine contained 

 a considerable number of diatoms. Sublimate to balsam. Fig. 104. 



105. Mesodorus cylindricollis n. sp. ^ ] - 7 ^ 1.9^1.7 '" Naked cuticle 

 traversed by exceedingly fine, plain transverse striae. Neck cylindroid. In 

 certain aspects, the amphids appear to consist of one circlet within another, 

 but are in reality true spirals. No doubt the papillae surrounding the mouth 

 opening correspond with folds in the lip-region; these, however, are so very mi- 

 nute as to be difficult of resolution. From the base of the onchium backward, the 

 pharynx is narrow and tapering, and joins the lumen of the oesophagus in an 

 indefinite way at a point distant from the anterior extremity nearly equal to the 

 diameter of the front of the head. From behind the pharyngeal swelling, the 

 oesophagus continues with about the same diameter until it expands to form the 

 rather obscurely pyriform cardiac bulb, which is fully three-fourths as wide as 

 the base of the neck, and contains a relatively large s^cph(14) Mj^ se(J6f6) 

 though rather simple valvular apparatus, having a diam- 

 eter half as great as that of the bulb itself. This valve 



is about twice as long as wide. The relatively narrow . ^ ( 



intestine joins the middle of the posterior surface of the M fljJaHBH^ 1 ~ 'j m ^ 

 cardiac bulb and soon enlarges so as to be two-fifths as _^ 



wide as the body. There is no distinct cardia. In cross- Sftwcph *750 9" 



section, the intestine presents six to eight cells. The lateral fields are about 

 one-fourth as wide as the body. Nothing is known concerning the renette or 

 the excretory pore. The nerve-ring surrounds the oesophagus squarely. The 

 tail of the male is strongly arcuate and conoid from the prominently raised anus. 

 The terminus is blunt and bears a simple spinneret. The caudal glands are 

 packed together in the anterior third of the tail, extending a little in front of the 



