FREE-LIVING NEMATODES 503 



64 (i) Posterior region of intestine atrophied; anus vestigial or absent. 



Family MERMITHIDAE . . 65 



The forms included in this group are of some size, being notably larger than those in the 

 first section of the nematodes. These often reach 10 to 20 cm. in length. They are more 

 or less opaque so that the internal structure cannot usually be determined by super- 

 ficial examination of the living animal. The intestinal region of the alimentary canal is re- 

 duced to a mere cord of cells without any cavity, or may be entirely wanting for a portion of 

 the length. The anus if discernible at all in the female has the form of a mere shallow dent 

 in the external surface of the cuticula to which the vestigial remnant of the intestine is attached. 

 In the male the terminal portion of the intestinal canal persists as the genital duct cloaca and 

 the anus functions as its orifice, but the intestinal tube is atrophied in front of the point at 

 which the sexual canal joins it. These forms are parasitic in larval life and do not feed during 

 the adult stage of their existence. The latter may be passed either in water or in the soil, 

 though the species are more frequently reported from the latter. By virtue of likeness in 

 habit and to some extent also in external form Mermithidae are often regarded as related to the 

 "hair snakes" (Gordiacea) to which, however, they bear no real structural resemblance. They 

 are the so-called " cabbage worms " which from time to time enjoy transient newspaper notoriety 

 on account of their supposed poisonous character whereas really they are harmless. 



The American Mermithidae are very little known. The following key to the established 

 genera will be of service to the student in allotting any of his discoveries to the proper genus. 



65 (66) Hypoderm with only two longitudinal fields; cuticula with criss- 



cross fibers; spicula two Neomermis von Linstow. 



66 (65) Hypoderm with more than two longitudinal fields 67 



67 (78) Longitudinal fields six 68 



68 (73) Cuticula without criss-cross fibers 69 



69 (70) Spicula two Mesomermis Daday. 



Representative species Mesomermis virginiana Cobb 1914. 



There are minute longitudinal striations throughout the body. These are interrupted on the 

 lateral lines where there is a distinct wing. There is no distinct pharynx. The mouth pore is 

 very minute and is located a little toward the ventral side of the middle of the front of the head. 

 The cuticula is penetrated on the head by a number of innervations which end in minute depres- 

 sions on the surface of the head. Near the mouth opening there is one of these depressions on 

 the dorsal side, and apparently a similar one on the ventral side, while nearer the outer margin 

 of the head there are two ventral submedian and two dorsal submedian similar depressions. 

 Pores occur also here and there on the body, as well as on the neck. The lateral organs present 

 the following appearance when seen from the side: They appear to project from the surface 

 of the body very slightly, beginning as a tube having a length about one-third as great as the 

 corresponding diameter of the head. This tube has very thin walls, and, a short distance in, 

 apparently near the surface of the body, a second element appears in the form of a circle inside 

 that representing the contour of the outer tube. This appears to constitute a sort of core in 

 the midst of which are a number of refractive elements, resembling nerve fibers, which pass in- 

 ward and backward toward the lumen of the esophagus. Some of these elements are longer 

 than others. The focus passing inward picks up one, then two, then several more, so that by 

 the time a view is obtained that is wholly inside the body there are seen a half dozen or more 

 of these elements. It is impossible in this view to pick up the internal connections of these 

 refractive elements. The lateral fields are about one-third as wide as the body. The tail of 

 the male bears several series of innervated papillae. These papillae are arranged on the ventral 

 submedian lines as well as on the ventral line. The ventral papillae just in front of and just 

 behind the anus are double. In the submedian rows there are four on the .tail one opposite 

 the anus, one a little farther back, a third near the middle of the tail, and a fourth considerably 

 farther back. In front of the anus on each side there are eight submedian papillae occupying a 

 distance more than twice as great as the length of the tail; the distance between the successive 

 papillae increases with the distance from the anus, so that the space between the seventh and 

 eighth is about two-thirds as great as the diameter of the body. Of the median papillae on the 

 tail there are three, two near the anus and one just in front of the middle of the tail, with pos- 

 sibly a fourth farther back. Of the median papillae in front of the anus there are two near the 

 anus, and ten additional ones about coextensive with the submedian papillae, and distributed in 

 the same manner. There are two outstretched testes, the posterior a little shorter than the 

 anterior. 



f~o ,-.2 *; - '|- a iM^ ^_ 4 !.. Habitat: Cranberry bog, Arlington Farm, Virginia. 



