146 BULLETIN OF THE 



It is difficult to believe that this canal represents merely the central 

 protoplasmic core upon which the scale was formed, since, if this were 

 the case, it would be closed terminally by at least a thin layer of cutic- 

 ular substance. But this is not the case. The opening is always larger 

 and plainer than the canal itself, which is too narrow to be measured. 



These structures are entirely lacking in the female. Their occurrence 

 in the male alone, and over only a limited area near the posterior end, 

 suggests connection in some way with the sexual act. If it be the case 

 here, as in Gordius, that the male grasps the female during copula- 

 tion by winding itself about the posterior portion of her body, the use of 

 these scales in holding on to the cuticula, which differs from that of 

 Gordius in being smooth, is at once suggested. The canal may then 

 be either the duct of a gland or a tactile organ. 



The cuticula of the female is nowhere more than 1 /a thick, and pre- 

 cludes thus any profitable study of its structure. The bristles are pres- 

 ent, and do not differ materially from those of the male. They are, 

 however, somewhat more slender and shorter. The scales of the male 

 are entirely lacking, and no analogous structures were found. 



h. Hypodermis. 



The hypodermis, or subcuticula, as it is often called in Nematodes, 

 forms immediately under the cuticula a layer of comparatively uniform 

 thickness and structure, being, however, peculiarly modified in the an- 

 terior chamber, in the median lines, and in the terminal organ of the 

 male. Its modifications will be considered under the organs in question. 

 Sometimes no trace of this layer can be found, but in the majority of 

 sections it can be demonstrated in some places. 



The hypodermis (Fig, 20) normally appears as a narrow granular layer 

 7 fx in thickness, without cell walls, but containing numerous prominent 

 nuclei arranged somewhat regularly, and characterized particularly by 

 the indefinite distribution of their chromatic matter and the faint, 

 uncertain way in which they are stained. It is separated from the 

 underlying muscular layer by a delicate basement membrane, which 

 ordinarily cannot be demonstrated, but which is easily seen where the 

 muscle cells are shrunk apart or torn away. 



Median Lines. — The hypodermis appears to be highly differentiated 

 in two regions, the dorsal and ventral lines, where it becomes so much 

 thicker as to cut down into the muscular layer and separate it into two 

 lateral areas. These lines were regarded by Verrill and Fewkes as 

 lateral ; but, as Burger has clearly shown, they undoubtedly correspond 



