CASTLE : NORTH AMERICAN RHYNCHOBDELLIDiE. 27 



tinues backward through the brain mass, eiidiiif,' in somite xiii. (Figure 1). 

 Within the pharyngeal sac lies the proboscis (pr'b.. Figure 1), which, in a state 

 of rest, usually extends from a point just behind the brain back into somite 

 XIII., where the ducts of the saliixiry glands enter its walls. These glands 

 {gl. sal., Figure 1) are a conspicuous feature of a Glossiphonia differentially 

 stained. They are always unicellular, and represent the largest cells found in 

 the body except certain nephridial cells and eggs approaching maturity. The 

 salivary gland cells have a great avidity for stains. They number in this 

 species thirty or more in each half of the body, and are found scattered through 

 about three somites (xii.-xiv.). The largest gland cells are those most remote 

 from the base of the proboscis. Each cell has a separate slender duct leading 

 into the wall of the proboscis and opening into the lumen of that organ at 

 some point along its length. 



A short slender oesophagus (as.. Figure 1), ordinarily lying entirely within 

 somite xiil., connects the base of the proboscis with the crop (i'glv., Figure 1). 

 This readily distensible part of the digestive tract extends over six somites 

 (xiv.-xix., Figure 1). Under ordinary circumstances it has but a single pair 

 of lateral diverticula ; these arise in somite xix. and extend backward, usually 

 ending in somite xxi. After a full meal, however, short lateral diverticula 

 may sometimes be seen also in the five more anterior somites (xiv.-xviii.), 

 but this condition appears always to be a transient one. 



The stomach (ga., Figure 1) begins in somite xx. and ends in somite xxill. 

 It bears four pairs of persistent lateral diverticula doubtless originally seg- 

 mental in origin, but now crowded within the limits of about three somites. 

 The first two pairs of stomach diverticula are directed forward, the last pair 

 backward ; the third pair lies about at right angles to the long axis of the body. 



The terminal part of the digestive tract, the intestine (in., Figure 1), is a 

 gradually narrowing tube ; it includes one or two proximal chambers separated 

 from the following part by constrictions. 



The anus is dorsal in position, as in all other leeches, and lies within or just 

 behind somite xxvii. (Figure A, page 32; Figure 34, Plaip 8). Comparison 

 with other species, in which the reduction of somites is less extensive, shows 

 that primitively the anus lay behind somite xxvii, 



/. Nephridia. 



The nephridia number at least sixteen pairs, possibly seventeen pair?. The 

 nephropores (nph'po., Figure 4) lie on the ventral surface of the body, somewhat 

 nearer the margin than the median plane, and almost exactly in the middle of 

 their respective rings. The nephropores are always found in this genus on the 

 middle ring of a somite. I have found them in sections of G. stagnalis in 

 somites vili.-xxiv., with the single exception of somite xiii. (ring 28). The 

 strong development of the salivary glands in this region may account for the 

 possible disappearance of the pair of nephridia which we should expect to 

 find here. 



