No. 2.] ANATOMY OF BDELLODRILUS ILLUMINATUS. 513 



cuticle nor cilia have been detected in this region. The mus- 

 cular coat of the oesophagus is principally made up of 

 thin, transparent, non-granular fibres, forming a sheet which 

 blends with each successive muscular septum, and is continu- 

 ous without much change throughout the remainder of the 

 alimentary tract. Circular muscles are distinguished as delicate 

 rings on the inner face of the longitudinal sheet, but become 

 much more conspicuous at the septal constrictions, where they 

 derive additional fibres from the septa themselves. 



The modification of the peritoneum to form chloragogue 

 cells begins in the third or second somite, behind which the 

 intestine is enveloped in a continuous layer to the seventh 

 somite, where they are absent (or sometimes sparingly scat- 

 tered among the peritoneal cells by which they are replaced), 

 but reappear in the eighth and ninth somites (Figs. 5, 12, 13, 

 and 15). In surface views of fresh material the chloragogue 

 cells appear as a mosaic of large polygonal cells, with straight 

 closely fitted edges, possessing a clear central nucleus, and 

 cytoplasm of a greenish brown color, due to the presence of 

 numerous large granules and minute globules. In sections 

 they appear more or less flattened, or prominently bulging, 

 according to their position and the degree of contraction of 

 the intestine. In the region of the dorsal blood vessel they 

 become elongated and arch over its walls. From their flat- 

 tened or concave bases protoplasmic filaments and columns 

 arise, which cross the peri-enteric sinus and bind the chlora- 

 gogue cells and the epithelium more firmly together. By the 

 increase of such strands in size and number the sinus is broken 

 up anteriorly and posteriorly into plexuses. The granules with 

 which the protoplasm is filled are stained deeply by most dyes; 

 and the clear globules above mentioned blacken with osmic 

 acid, while unaffected by ordinary stains, and dissolve in chlo- 

 roform, etc., appearing in sections as spaces. Their evident 

 fatty nature leads me to regard the chloragogue cells as ab- 

 sorptive, while, on the other hand, their relation to the peritoneal 

 corpuscles renders an excretory function probable. There seems, 

 then, little choice between the two opposing views which have 

 been brought forward, both probably being in part correct. 



