198 FILTER-BED NEMAS 



certainty; however, innervated papillae occur near the terminus, doubtless 

 tactile in function. The shortest, i.e., dorsal, unpaired caudal gland empties 

 through a dorsally left submedian duct. Of the two longer and paired glands, 

 one, the left submedian, empties through a ventral ampulla, while the other 

 empties through a dorsally right submedian one; the details of the debouchment 

 remain somewhat obscure and no attempt has been made to indicate all of them in 

 the illustration. The three pores, however, are just in front of the "equator" of 

 the valve. 



Digonic. This species presents the unusual peculiarity for an hermaphroditic 

 nema of developing its ova in one gone, and its sperm in another gone of much 

 smaller size, in a word is digonic. So great is the disparity between these two 

 branches of the sexual apparatus that at first glance one almost inevitably con- 

 cludes that the very small posterior branch is a mere functionless vestige. 

 A careful examination seems to prove that only ova are produced in the anterior 

 branch, while the very small outstretched posterior gonad functions as a testis; 

 the evidence for this latter conclusion being the occurrence of spermatozoa and 

 spermatocytes in small numbers arranged in the order to be expected if the 

 organ were a small gonad devoted solely to the production of sperm. The cells 

 in this minute gonad are so few that their precise order is not a striking feature, 

 and yet an examination of a series selected from among individuals in which the 

 ova in the anterior gonad are still quite young and small, enables one to demon- 

 strate that the cells near the blind end of the small gonad correspond in structure 

 with primary spermatocytes, and that the succeeding cells, sometimes as few as 

 two to three in number, represent successive steps in the development of the 

 spermatozoa. Occasionally one finds here a pair of gonic cells lying side by side, 

 each containing about six chromosomes, practically as definite as those to be seen 

 in the testes of male individuals of typical free-living amphigonic nemas. Often 

 the perfected spermatozoa appear not to exceed eight to twelve in number. 

 There is an obscure tendency for them to be located in groups of four, such as 

 should exist if they were produced in situ in quartets in the manner character- 

 istic of the spermatozoa of nemas. Once an egg was observed containing near 

 its equatorial periphery a body corresponding in size and staining properties to 

 one of the spermatozoa to be seen free in the uterus. The nucleus of this egg 

 showed signs of being affected by the presence of the spermatozoon, though it 

 appeared not yet to have produced polar bodies. All these appearances are in 

 harmony with the supposition that the posterior branch of the sexual apparatus, 

 small as it is, functions as a testis. 



TRIPYLA Bastian 1865 



3. Tripyla monohystera de Man. /o [79 T. 271 T7? 1 ' 4 """ Few nemas 

 are more agile than this. Its movements are extremely rapid, especially those of 

 the head end. It is unusually flexible, coiling and uncoiling all parts of its body 

 with great rapidity. It is of a restless disposition, at least so appears when 

 brought under the microscope for examination. 



I have often seen this Tripyla attach itself to glass and then exhibit the evolu- 

 tions characteristic of nemas possessing well developed spinnerets, but in spite 

 of careful examination of living specimens, and specimens preserved both in 

 glycerine and balsam, I have seen no definite traces of caudal glands. The 

 cephalic setae are segmented and consist of two or more joints. 



Harbors a Parasite. Tripyla monohystera of the Washington filter-beds often 

 contains what appears to be a peculiar spherical parasite. The parasites (?) 



