of the Fishery Board for Scotland. 



111 



that the variations arc due to the delicate terminal spine being broken off, 

 and the different conditions noted and drawn in the figures may be stages 

 in the regeneration of the extremities of the hairs. This repair would 

 appear to be continuous. 



The hair is tubular, and in the central cavity or core there is a large 

 quantity of minute oval corpuscles. 



The shell of the hair consists of two main thick layers, viz., an outer, 

 oi., and an inner, figs. 30 and 32. They are laminated in structure ; 

 the outer layer shows a division into one, sometimes two, thin cuticular 

 layers ; and the inner layer usually shows a separation into one thin layer 

 on the outer side, and sometimes also a thin layer next the core. The 

 internal surface of the inner layer is uneven, corrugated in appearance. 

 The inner layer varies in thickness in different parts of the hair : at the 

 base it is especially thick, fig. 30. It is practically a replica of the outer 

 layer. The two layers are to some extent independent, or at least 

 separate easily from one another. This is seen when a hair is broken. 

 It often happens that when the outer layer is snapped, the inner layer 

 remains intact, and the two parts of the outer layer become separated 

 by an interval, vid. fig. 6. It does not appear that the separation of the 

 broken halves of the outer skin is due wholly to a sliding over the inner, 

 but rather also to the fact that the inner layer expands on the release 

 afforded by the rupture of the former. 



The anterior surface of the endopodite has scattered over it short, stiff 

 hairs, fig. 50. 



The endopodite is jointed at about a fourth of its length from the base, 

 and at this point there are muscles for moving the distal portion. The 

 latter bears the greater mass of the hairs. 



The Exopodite. 



The exopodite resembles somewhat the endopodite in form. It is, 

 however, more flattened in its proximal part than the latter. With the 

 exception of the fourth, the exopodites are more or less twisted on their 

 axes in such a way that the edges bearing the hairs are brought into 

 an obliquely antero-posterior position, vid. fig. 13. 



The exopodite is furnished on either side from base to tip with a very 

 thickly set row of plumose hairs. These are of various length, vid. figs. 

 11, 12, 35, and 36. In the case of the shortest hairs, the ciliation 

 commences close to the base, while in the others it begins further along 

 the stem in proportion to the length. In the case of the longest hairs 

 almost the whole of the proximal half is bare of cilia, fig. 36. 

 Through the closely set arrangement of the hairs of different lengths, the 

 short hairs supply the ciliation which is absent from the stems of the long 

 hairs. In this way there results the formation of a thickly-set hedge, 

 with no unnecessary overlapping of structures. The ciliation is at first 

 sparse, but quickly increases in amount. 



The cilia are all long, stiff, terminating in fine points ; they are more- 

 over serrated. On the shortest hairs they are long and slender, fig. 8 ; on 

 the longer hairs flattened, lanceolete in shape, fig. 7. They are arranged 

 all round the stem of the hair, recalling generally the structure of a test- 

 tube brush. At the extremity of the hair, in consequence of the 

 shortening of the nodes, the cilia are packed closely together round the 

 falcate tip. 



The stem of the hair is tubular. The core is narrow, the wall thick 

 and composed of several layers, fig. 9. Fig. 17 shows an ocular section 

 at the base of the hair. The tube of the hair is continuous with a canal 

 in the exopodite*. 



