354 MARIONELLA 



the base of the head, which is more prominent than the others. The somatic 

 setae appear always to be reduced to innervations. There are no conspic- 

 uous pores on the surface of the body, but the ellipsoidal glandular cells of 

 considerable size invariably found in the lateral fields are connected with 

 the exterior by means of very small and inconspicuous pores. 



Head and pharynx. The somewhat rounded to subtruncate head is us- 

 ually continuous with the neck, but is sometimes set off by a slight contrac- 

 tion, or by a very slight, broad, shallow constriction. The lip-region, on 

 the other hand, is nearly always set off by a very slight, narrow and shallow, 

 but usually distinctly visible constriction. The membranous lips are them- 

 selves thin and confluent, and apparently close by virtue of their elasticity. 

 Their margins are very finely striated and possibly sometimes fimbriate. 

 The lips are supplied externally with six forward-pointing papillae (or six 

 sets of papillae), arranged in a single circlet having a diameter about one- 

 half as great as that of the lip-region. These papillae are so exceedingly 

 small as usually to escape observation. Their innervations are also exceed- 

 ingly inconspicuous. Usually it is only when the papillae happen to project 

 forward a little in exact profile that they come into view. 



At first sight the pharynx appears to have the form of that of Oncholaimus. 

 It is, however, nearly always divided into two distinct chambers of more or 

 less equal length, the anterior of which is somewhat the wider and the more 

 symmetrical. This regular anterior chamber is nearly always a napiform 

 cavity one-half to two-thirds or even three-fourths as wide as the correspond- 

 ing portion of the head. The posterior chamber is of smaller size, usually 

 only about three-fourths as wide as the anterior chamber, and more or less 

 irregularlv spheroidal in form. The refractive walls of the pharynx are 

 well-developed, but not very thick. The pharynx is usually armed with a 

 single well-developed, forward-pointing onchinm, but there may be one or two 

 additional smaller onchia in exceptional cases. The apex of the main, and 

 usually only, onchium, always occupying the right ventral submedian posi- 

 tion, extends forward sometimes as far as the lips. The convex-conoid, 

 enlarged base of the onchium fills the posterior chamber of the pharynx 

 comparatively full. This enlarged portion of the onchium is continued in 

 the front chamber by a narrower, more slowly tapering, convex-conoid, 

 more or less acute summit. This organ is perforated and so serves as the 

 outlet of a large oesophageal gland. The posterior pharyngeal chamber is 

 separated from the anterior by a constriction, marked in its most pronounced 

 form by the presence of narrow and refractive, transverse, arcuate elements 

 or thickenings, placed end to end in a circle. Adjacent to this circle, usually 

 in front of it and close together, there are one to three transverse rows of 

 denticles, each consisting of either about thirty-two, or about sixty-four 

 to eighty, somewhat forward-pointing units. These more or less inward 

 pointing denticles are rather acute, cylindroid-conoid, uniform in size, and 

 are usually so minute as to be barely resolvable with high powers of the 

 microscope. 



When viewed from in front, the pharynx is seen to be very nearly round. 

 The margin of the lip-region is so thin and filmy that oftentimes it is difficult 

 to delimit. An exact count of the denticles in a specimen of an unpublished 

 but typical species, gave the following figures: anterior series of denticles 

 62 ; second series 62 ; back series of larger denticles 20 ; this decreased number 

 in the back row being due not only to the fact that the denticles are larger 



