188 ORIGINAL ARTICLES. 



The cuticle covered the superficial surface of the tubercles and 

 extended for some distance up the sides of the spines, although I 

 never saw it passing over their free ends. It was continued from 

 the outer surface of one tubercle to that of the adjacent ones, over 

 the serrated aj)posed margins. In it, and in it only, the pigment of 

 the skin was contained. 



The deeper hard part of the tubercle, which OAved its great 

 density to the deposition of a calcareous, or other inorganic, material 

 in its substance, formed the chief portion of the tubercle, and the 

 spine projecting from it. It presented very slight traces of structure, 

 a few taint lines, running for the most part horizontally, constituting 

 the only markings on it. The spine had a closely similar aspect, 

 and in many cases appeared to possess a cavity in its interior. 

 In the spine faint lines might be seen, extending in a direction parallel 

 to its long axis. When the tubercles were acted on by hot caustic 

 potash, they were entirely broken up and resolved into a number of 

 particles, some of which were elongated, others irregidarly shaped, 

 respecting the nature of which it would be difficult to give a positive 

 opinion. When a portion of the skin was digested in warm caustic 

 potash the tubercles separated from the cutis, whilst the cuticle still 

 remained connected to their outer surfaces. The inference might be 

 drawn from this, that the hard part of the tubercles, like the cuticle, 

 was an e})idermal, rather than a dermal structure. Such an inference 

 might possibly, however, be erroneous, as the separation along this 

 line might perhaps be due to the alkali acting more readily on the 

 fibrous cutis than on the diflierent parts of the tubercle. An absolute 

 opinion as to the homology of the tubercles could only be given by 

 tracing the manner of their development. 



By digestion in hydrochloric acid the inorganic material was 

 dissolved out of the hard part of the tubercle. 



ILLUSTRATIONS. 



Plate VI. — Fig 4. — Fibres and cells of cutis. X 200 diam. This figure simply 

 gives the anatomical elements of the cutis, as seen in a jwrtion which has been 

 dissected with needles. The cellular element bears a larger iDroportion to the fibrous 

 element tlian has here been represented. 



• Fig. 5. Surface view of integument, showing serrations at margins of tubercular 

 plates, central sjiines, and various forms of pigment arrangement. X 4,5 diam. 



Fig. 6. — Section through tubercular plate with its spine, and subjacent cutis. 

 X 120 diam. 



