490 Illhiois State Lahoratori/ of Natural History, 



above mentioned and differing somewhat in size and distance 

 apart. They are generally single but here and there are 

 grouped in twos, threes, or fours. The number in a transverse 

 row counted singly or as groups is from thirty to fifty on the 

 middle region of the body. A feAV others may be scattered 

 between the rows or even form a third broken row between the 

 larger papilla3, particularly on « 3. Along the margins large 

 numbers may be aggregated. The large rough papillfe are 

 prominent wart-like elevations of the integuments, some of 

 which measure more than a millimeter in height in living 

 examples. They appear not to contract under ordinary stim- 

 uli, but are sometimes very much less elevated in preserved 

 material. They are generally conical in shape, their summits 

 bearing a ring of from four to twenty smaller sense papillae 

 arranged around a central larger one. When the number is 

 greater than eight or nine they are likely to form a less regular 

 ring and to extend further down the sides of the wart, wdiile the 

 central one becomes replaced by two or three. A relation 

 between the size of the wart and the number of papilla? in its 

 crown seems to exist. Of the median series (7«j9) that on « 2 

 is the largest and often bears twice as many sense organs as 

 that on al, which is the smallest. The next series counting 

 laterad {rndp) is always represented by a very large wart on 

 « 3, by a much smaller, frequently absent, one on a 1, and 

 on « 2 is replaced by a rather prominent but smooth papilla 

 which supports the dorso-median sensilla {md). This cannot 

 be confounded with the rough papilbf . The next important 

 series {dip) is made up of a large one on a '2, a smaller one 

 on a'd, and a very much smaller one or none on a 1. Just 

 external to the large one on a 2 is the dorso-lateral sensilla 

 {dl), which is somewhat elongated transversely and is litttle 

 elevated above the surface. At the margin are two rows 

 so imperfectly developed that they are probably better 

 descri'bed as a single irregular row (dvip) sometimes repre- 

 sented by two warts on a single annulus. Warts of smaller 

 size are generally present, but are more irregularly distrib- 

 uted than the fairly constant ones just described. They are 

 most frequent on a 1, where one such is likely to be present 



