386 PROCEEDINGS OF THE ACADEMY OF [May, 



of valves in the lateral arches. Usually the arches in III and IV have 

 1 set, V 1 or 2 sets ,VI 3 or 4, VII 4, VIII 4 or 5, IX and X 6 or 7, and 

 XI 6. The right arch in X sends a loop into the sperm sac as far as 

 the diaphragm present in the immature worm, while that of XI enters 

 the ovisac and breaks up into a rich plexus. The intestinal plexus 

 reaches as far forward as VII. 



Owing chiefly to the height of the coelomic endothelium the body 

 walls are thick and opaque. Peritoneal corpuscles (fig. 10) are of two 

 forms, about 90 per cent, of them being spherical and filled with rounded 

 opaque granules having nearly the color of the vertebrate red blood 

 corpuscle. The corpuscles measure .01 to .015 mm., and the granules 

 .0012 mm. in diameter. The corpuscles are much less abundant than 

 those of Monopylephorus glaher, and are easily distinguished by their 

 smaller and more numerous granules. With the spherical corpuscles 

 are associated a number of nearly homogeneous, colorless, flattened, 

 fusiform corpuscles and a few leucocytes. 



The brain is about as broad as long, very massive and with a slight 

 median emargination posteriorly, and prolonged anteriorl}^ into a pair 

 of relatively slender lobes separated by a deep cleft. 



Like so many other organs the nephridia have much in common with 

 those of Monopylephorus glaher. The funnels are provided with a 

 tongue which, however, is short and broad, and the remainder of the 

 funnel is much lobulated. Nearly sessile on the septum, it passes into 

 a short and narrow postseptal neck which, in turn, enters a large 

 tubule with a very wide irregular lumen and highly granular walls 

 which is doubled on itself and forms, with the first section of the tubule 

 loops, the so-called glandular portion of the nephridium. The tubule 

 loops have ciliated ampullae and are in general arranged as in M. glaher, 

 but their folds are much more open and in the posterior nephridia reach 

 through two somites. The efferent canal springs from the glandular 

 mass and opens to the exterior in front of the ventral setae. Altogether 

 the nephridium is of the true tubificid type. They are frequently 

 developed on one side onl}'- or altogether absent from many somites. 



The spermathecse (fig. 8) are large, with prominent simple ellipsoidal 

 ampullae, varying much in size and shape with the degree of distension, 

 but usually filling a large part of the coelome of X, and reaching to the 

 dorsal level of the intestine and the septum ^^. There is always a well 

 differentiated muscular duct without glands, short in distended sperma- 

 thecae, but relatively long in empty ones. There are no spermatophores, 

 the spermatozoa being free and loose. 



The male organs (fig. 7) are remarkable as combining the short sperm 



