THE ANATOMY OF PENTASTOMUM TERETIUSCULUM. 7 



are the two large ones now described to the internal pair, and 

 these again identical in structure with others having no claim 

 whatever to be regarded as modified appendages. It would 

 appear from the above that very probably this single pair of 

 papillae, which are directly homologous with the smaller 

 ones, has become specially modified and enlarged in connec- 

 tion with the external opening of the hook- gland, and that, 

 agreeing with Stiles, they are not to be regarded as modified 

 antennae. 



{b) Secondary Papillae (figs. 3, 3, and 5). — These consist 

 of seven pairs of minute papillae, which appear under the lens 

 as small white spots on the dorsal surface. They are distri- 

 buted as follows : 



(1) A pair close to the anterior end of the depression 



containing the external pair of hooks (figs. 2 and 3). 



(2) A pair placed somewhat posteriorly to the latter (3). 



(3) A pair placed posteriorly to the latter and nearer to 



the median line (4). 

 On the lateral surface : 



(4) A pair, one placed to the outer side of each of the 



external or outer pair of hooks (5). 



(5) A pair, one placed on each side of the body in a line 



with (4) and the lateral line of the body (6). 

 On the ventral surface : 



(6) A pair, one placed on each side immediately in front 



of the first annulus, and corresponding in position 

 to the interval between the two hooks on either 

 side (7). 



(7) A pair, one placed on each side in the first annulus, 



and corresponding in position to the hook nearest 



to the mouth (8). 

 In addition to the above, there can in some specimens be 

 detected what is apparently a line of minute papillae, of which 

 a pair is present on each segment for perhaps the most 

 anterior eleven. These are placed along what is called the 

 " lateral line," where the body-wall is slightly thinner than 

 elsewhere, and becomes on contraction of the animal thrown 



