88 CALIFORNIA ACADEMY OF SCIENCES. 



narrow excretory tube with thick walls. Nearest the male pore this tube is quite 

 straight, or only slightly folded, but at its distal end the windings are greatly packed 

 or irregularly coiled (fig. 99, tube). 



The part posterior to the penial collar I have designated the atrium proper, 

 simply because it does not contain any inner layer of glandular cells, and because in its 

 distal end it connects with the true prostate. The excretory tube continues all through 

 this part and is, so to say, suspended in a more or less dense mass of fibrous tissue. 

 Nearer the collar this mass is reduced to a few strands only, but towards the distal end 

 it becomes quite dense, especially so nearest the tube, while towards the periphery it is 

 much less dense (fig. 92,/. (.., fibrous tissue;/. sL, fibrous strands). Fig. 100 repre- 

 sents a cross-section taken near the distal end; tlio tube is seen coiled in the center, 

 while fibrous tissue connects it with the walls of the atrium. 



The exterior layers of the atrium are constructed very much as the same lay- 

 ers of the prostate proper and the storage chamber. There are three layers which 

 are common to the two different parts of the prostate. Interiorly a thin layer of cir- 

 cular muscles somewhat variable in thickness in different parts, but generally only 

 three or four sti'auds thick. Exterior to this layer runs a spirally wound layer of lon- 

 gitudinal muscles, arranged in band-like plates, and when seen in cross-section re- 

 sembling a row of fringes (figs. 100, 101, 102, 103, lOG, 107, 1, m). Fig. 107 shows these 

 plates, highly magnified, to consist of rather rectangular muscular strands. Exterior 

 to this layer of I. m. muscles we find everywhere a broken row of prostate glands of 

 very minute size, appearing to penetrate in between the muscular plates, though on 

 account of the macerated condition of the tissues I could not follow their tubes. These 

 small glands, which barely project outside of the muscles, are found everywhere from 

 the distal end of the storage chamber to the penial collar, wherever this muscular 

 layer is found. In places they are continuous, in others scattered about, seldom more 

 than one row thick (fig. 10l,(/ls). But as we reach the region of the narrow part of 

 the prostate and especially the part of the storage chamber where the spermducts 

 enter, we find another thicker layer of prostate glands similarly scattered over the 

 longitudinal muscular fringe (figs. 102, 103, 106, 107, pr. gl. s, small prostate glands; 

 pr. ql. L, large prostate glands). In the region where the spermducts enter the stor- 

 age chamber this layer of large prostate cells is almost continuous and considerably 

 thicker than the muscular layers combined (fig. 103). 



The prostate proper contains besides these layers of muscles and exterior 

 prostate glands two inner layers, which resemble and propably correspond to the two 

 cell-lay^ers found in the prostate of the higher oligochreta, viz.: one layer of lining 

 epithelium (fig. 101) and one layer of glandular prostate cells, with very large nuclei, 

 and separated one from the other by transparent spaces, through which possibly enter 

 projections of the exterior prostate glands. These two characteristic layers do not 

 extend to the narrowest part of the prostate. Hence the muscular layer is covered 

 by a single row of inner lining epithelium with large, slightly oblong nuclei (fig. 

 102), which in the very narrowest part are about 12 to 14 in the row. 



The proximal end of the storage chamber is lined by a very thick epithelium 



