132 bulletin: museum of comparative zoology. 



boscis, and that the darkly staining secretion was formed elsewhere 

 and has accidentally lodged on the flagella of the sensory cells. This 

 hypothesis is merely a tentative one, however. 



The middle chamber extends backward about as far as the 

 nephridial region, and is there succeeded by the posterior chamber, 

 the epithelium of which is of the glandular type characteristic of 

 the proboscis. In the posterior chamber occur also tjqjical rhabdite 

 cells. These are situated on one side of the lumen only, and are 

 not very numerous. In form each rhabdite cell (PI. 11, fig. 72) is 

 pyramidal, with the apex much elongated and bearing a single 

 nucleus as usual. The base of the cell borders the lumen and bears 

 a single layer of spindle-shaped rhabdites («) to the number of per- 

 haps 20 to 50 (PI. 11, fig. 72) . The transition of the epithelium of 

 the middle chamber into that of the posterior chamber is not abrupt, 

 for the glandular and rhabdite cells only gradually replace those 

 which bear the flagella. 



The middle chamber has a rather thick layer of connective tissue 

 (PI. 11, fig. GO, ct) and a homogeneous basement layer {bm), both 

 of Avhich lie between the circular and the longitudinal muscles. 

 The connective-tissue layer is the more internal, and is provided 

 with nuclei and delicate fibrils, while the basement layer which lies 

 just internal to the longitudinal muscles is perfectly similar to that 

 which was found external to the longitudinal muscles in the wall of 

 the anterior chamber. In the posterior chamber the layer of con- 

 nective tissue is wanting, while the homogeneous basement layer 

 has again moved outside the longitudinal muscles and taken up a 

 position immediately internal to the outer, flattened epithelial layer. 

 The .conditions are thus exactly as in the anterior portion, except 

 that the basement layer is very much thinner. Toward the pos- 

 terior end of the proboscis all the layers, except the glandular 

 epithelium and longitudinal muscles, become so much reduced as to 

 be hardly demonstrable. 



Intecjument. — As in related genera, the integument is remarkably 

 thick in proportion to the other layers in the anterior portions of 

 the body. The relative thickness in different parts of the body is 

 shown in PL 6, figs. 53, 54, PI. 7, figs. 55, 56, PI. 8, figs. 57, 58, and 

 PI. 9, figs. 59, 60. In the intestinal region the integument becomes 

 decidedly thinner than more anteriorly, and it is usually cons|)icuously 

 thicker on the dorsal than on the ventral surface of the body. The 



