JUNE 19, 1932 COBB: METONCHOLAIMUS PRISTIURUS 443 



rather indiscriminately, and to extract its nutriment from a variety of organic 

 material contained in the mud. Large quantities of this food material in the 

 intestine may interfere with microscopic examination; hence the advisability 

 of keeping the nemas in clean cool seawater for a day or two before examina- 

 tion. The cardiac collum, or constriction, 13, between the oesophagus and 

 intestine, is about two-fifths as wide as the base of the neck, making a very 

 obvious demarcation between the oesophagus and the intestine. There is a 

 conoid cardia, 14, about two-fifths as wide as the base of the neck; this is the 

 very short extension of the oesophagus into the intestine, and is composed of 

 numerous smaller cells of a distinct kind, having to do, among other things, 

 with the prevention of regurgitation. Though small, the cardia is a very 

 important part of the alimentary canal. The outer portion of the intestine, 

 1, 76, is usually more or less destitute of granules, but the inner and greater 

 portion of each intestinal cell contains globular yellowish granules, 69, of 

 variable size, the largest of which are about three microns in diameter, and 

 the smallest less than one micron. These granules are varied and numerous, 

 sometimes are even packed close together, and may be so arranged in the cells 

 as to give rise to a faint, or sometimes a quite distinct, tessellated effect. 



The intestine is made up of cells of different kinds, discharging different 

 functions. One of these various kinds is readily made out, especially with the 

 aid of polarized light, namely the cells, as many as one hundred in number or 

 even more, containing the exceedingly minute Urefringent granules. These 

 cells, 15, 81, 98, when examined by ordinary transmitted light, present a 

 finer texture internally, and usually are more distinctly yellowish. If a suit- 

 able specimen be allowed to remain in a concentrated solution of seawater- 

 methylene-blue a few minutes, a differential staining of the "birefringent" 

 cells will often occur, but the effect does not last. The "birefringent" cells are 

 everywhere less numerous than those that do not contain birefringents, and 

 there are none of them at all in the posterior part of the intestine. We may 

 therefore speak of two distinct intestinal regions, one fore, one aft. The 

 "birefringent" cells occur in early ovic embryos. 



The rather prominent short rectum, 19, the rear part of the intestine, is 

 somewhat cuticularized, and is about as long as the anal body diameter; from 

 the somewhat depressed anus, 70, it extends inward and forward at an angle of 

 about forty-five degrees. Its structure in the female differs somewhat from 

 that of the male, which appears "helical." The anterior and posterior lips of 

 the anus are of about equal size. Small inconspicuous somewhat pear-shaped 

 unicellular anal glands can sometimes be seen, lying alongside the rectum with 

 their narrowed necks directed toward the anus. 



Tail and spinneret. The slightly arcuate tail is first conoid, then cylindroid 

 in the posterior fourth, where it ends in a somewhat blunt, almost impercep- 

 tibly swollen, rounded spinneret, 73, armed only with three exceedingly incon- 

 spicuous setae, two ventrally submedian, 74, and a dorsal one, 24. Though 

 insignificant in appearance these sensory setae are important. The very 

 nearly symmetrical spinneret displays internally the three very slightly 

 swollen ampullae of the three caudal glands, 23. The spinneret valve, or plug, 75, 

 four microns across, almost at the very end of the tail, stains green with 

 methyl blue ("intra vitam") while other nearby parts stain blue. This impor- 

 tant valve is hemispherical posteriorly and tapers anteriorly to a fine contractile 

 element, shown white in the drawing, fastened in the midst of the three ampul- 

 lae (23). It is by the contraction of this minute fiber that the plug or valve is 

 pulled away from its seat, so as to permit the sticky, non-water soluble, 



