690 PROCEEDIXGS OF THE ACADEMY OF [DeC. , 



the body wall, figs. 1, 16, t/, and posteriorly ends blindly about 

 .8 mm. in front of the anus, fig. 17, Re. 



In the brain region the rhynchocoel i3 very narrow, passing 

 between the dorsal and ventral commissures, fig. 20, Re. A con- 

 stant widening of the rhynchoccel takes place in the esophageal 

 region, fig. 22, and the widest, most expanded part usually lies above 

 that portion of the body extending from the nephridia to the 

 beginning of the middle intestine (see fig. 1). At the latter 

 point the great increase of the circular muscle layer of the probos- 

 cis sheath and of the inner circular layer causes a sudden con- 

 striction of the rhynchocoel, fig. 23. Posterior to this narrowed 

 region, which is quite short, the rhynchocoel again widens, then 

 gradually narrows more and more until near the end of the body 

 the cavity is scarcely demonstrable. 



The rhynchocoel is filled with a fluid in which float numerous 

 long narrow cells, fig. 43, the " rhynchocoel corpuscles" of Biir- 

 ger, " Navicula " of Quatrefages (1846) and Keferstein (1862). 

 These cells are long and spindle-sha^Ded, larger in the middle 

 where the nucleus lies, and tapering to a fine point at each end. 

 They are flattened and ribboulike, as may be seen when the cell is 

 twisted. Biirger (1892) has described an "attraction sphere" 

 in the cytoplasm by the side of the nucleus. These do not appear 

 in my preparations and, unfortunately, the rhynchoca^ corpuscles 

 were not studied in life. In one cell, however, the nuclear mem- 

 brane curves in on one side, and a lighter zone in the adjoining 

 cytoplasm may be seen, but there are no astral radiations. In 

 another cell, fig. 43, jS\, two nuclei are present, probably the 

 result of amitosis. 



A second, smaller type of cell, fig. 42, is also found in the 

 rhynchoc(cl, resembling the free corpuscles in the blood vessels. 

 These cells are rouTided, with finely granular cytoplasm and 

 prominent nuclei. 



The layers of the proboscis sheath are as follows (see figs. 20, 

 50;: 



1. The circular muscle layer, C.M.p.s. 



2. The longitudinal muscle layer, L.M.p.s. 



3. The basement layer, B.L. 



4. Tli(! epithelium, Rc.Ep. 



The muscular layers are rather thin in the head region, except 



