1(30 (S. S. 462) 



THE MONONCHS 



17. M. tunbridgensis Bastian. The Tunbridge mononch is interesting histori- 

 cally as well as intrinsically, for it was an examination of numerous specimens of 

 this aquatic nema that marked the beginning of the classical researches of the 



6.7 24. '52' 20 



2.4 

 2.1 

 2.4 



2.8 



7.8 



24. 



3.6 

 23. 



3.7 



89. 

 2.3 - 



90. 



1.3 n 



2. 3.5 ?.6 ?.7 1.7 



well-known English nematologist, H. 

 Charlton Bastian. The upper formula 

 is the average of glycerine specimens 

 from the Arlington Farm, Virginia, 

 U. S. A., while the lower formula is 

 the average of the writer's balsam 

 specimens from Tunbridge Wells, Eng- 

 land. As a rule the 4iead is rather suddenly contracted opposite the pharynx, and 

 this is perhaps the best distinguishing mark of the species. Bastian, who had an 

 abundance of specimens, emphasizes this character. The adjacent figures are those 

 of Dr. de Man, and show the pharynx relatively a little narrower than is usual. The 

 tails of the writer's Tunbridge Wells specimens accord rather with Bastian's figure 

 than with his description. As is often the case in other mononchs, the labial papillae 

 stain more strongly with carmine than do adjacent tissues, so that the lip region as 

 a whole appears strongly colored. Opposite the dorsal tooth there is an exceed- 

 ingly minute, low, subventral projection. The form of the amphids is not fully 

 determined ; they are located nearly opposite the base of the pharyngeal tooth, and 

 have a width one-half to one-third as great as that of the pharyngeal cavity. Near 

 the cardia the cesophageal lining occupies about one-fourth of the optical longitudi- 

 nal section of the oesophagus. The intestine, which ma}' present a certain amount 

 of tessellation, is about 10 to 12 cells in girth. The anterior two-fifths to one-half 

 of the tail is conoid in such a fashion that at the middle the diameter is about 

 one-sixth as great as at the anus. Thence onward the tail is nearly cylindrical, and 

 ends in a very slightly expanded terminus armed with one or two very inconspicuous 

 papillae. That a sticky substance often exists on the surface of the terminus of the 

 tail is evident from the accumulation there of minute particles of foreign matter. 

 Caudal glands appear to exist immediately behind the anus, but their nuclei have 

 not been definitely made out as yet. The lateral fields appear to be one-third as 

 wide as the body. Each ovary contains a score or more of developing ova, ar- 

 ranged in several tiers in the distal half of the organ, but single file elsewhere. 

 The somewhat elongated eggs are about one and one-third times as long as the 

 body is wide, and about half as wide as long, and occur in the uteri one at a time. 

 This seems to be primarily an aquatic species, though the writer has found it also 

 in soil in the vicinity of rivers and streams. Fig. 30 (after de Man). 

 18. M. truncatus Bastian. CEsophagus conoid, its lining well developed. Intes- 

 2.5 ? 25. '50+* 86. tine about 12 cells 



? if; sTa 3.4 ' 1 - 8 BB i n girth, more or 

 ? 25. M 92.\ less distinctly tes- 



? ? ? ? ' sellated. Lateral 



fields broad and distinct. It is a question whether to 

 retain this species on the basis of Bastian's original 

 description, or to accept Biitschli's description as a 

 rehabilitation of Bastian's species. It is hardly likely 

 that any species of Mononchus is destitute of labial 

 papillae, and in this respect Bastian's description 

 seems defective. The extreme reduction of the 



