lOO CALIFORNIA ACADEMY OF SCIENCES. [Proc. 3D Ser. 



i. gr. represents the part of the epithelium facing the inter- 

 segmental groove, while ex indicates the convex part. The 

 great majority of the cells are long and narrow, tapering 

 from the cuticle. 



Figure 22 represents a single cell. Of these cells there 

 are two different forms: one has a short nucleus in which is 

 always seen a large central nucleolus; the nucleus of the 

 other is longer and narrower, generally without any nucleo- 

 lus. The cytoplasm of the two cells differs; it is agglomer- 

 ated behind the nucleus in one, but is not so placed in the 

 other. This cytoplasmic clot stains a brilliant red with thio- 

 nin, just as do the nuclear chromosomes of the several cells. 

 The structure of these cells points to a difference in func- 

 tion also, and undoubtedly they serve a purpose other than 

 that of supporting cells. I believe them to be some kind of 

 sense-cells. The free distal ends are drawn out finely and 

 are frequently seen penetrating the basal membrane separat- 

 ing the epithelium from the muscular layers, finally losing 

 themselves among the muscles and connective tissues. The 

 cells cannot be organs of smell or taste, because they do 

 not end in sense-hairs; but they are eminently adapted to 

 function as organs of touch, and are probably especially sen- 

 sitive to vibrations. Their free ends offer an unusually large 

 surface to the exterior. The distal ends, which are very 

 thin, project beyond the regular line of the epidermis 

 and connect with nerve-fibres. Similar cells are found 

 among the goblet and supporting cells of the epidermis of 

 the general body-wall, but they are present there in small 

 numbers. I also find such cells to be numerous in the 

 cephalic lobe of many species, a proper location, the prosto- 

 mium being principally an organ of touch. The decreased 

 number of supporting cells, the narrowness of the somites, 

 enabling twice the number of nerve-centers to be present 

 in the same space, and the great number of " touch cells" 

 would, therefore, it seems to me, make the caudal zone 

 especially sensitive to vibration or to touch, and increase 

 its efficiency as an, organ of touch. 



