154 Mr. A. Tulk on the Anatomy 0/ Plialangium Opilio. 



thorax, upon the sternal plate, and the first dorsal and ventral 

 segments of the abdomen. 



It consists of three layers, which, being but loosely adherent, 

 may be readily separated from each other. The outer, or epidermis, 

 is colourless and transparent, and made up of numerous minute, 

 irregularly conical and projecting cells, closely set upon a subja- 

 cent connecting membrane, but not in contact with each other. 

 Besides these, there are other larger, more opake and prominent 

 cells, scattered less freely over the rest of the integument, and 

 prolonged here and there to form short spines. Lastly, a set of 

 large, more or less obtusely conical, flattened or papilliform emi- 

 nences are distributed, few in number, and with regularity wher- 

 ever they occur, and are remarkable for having a single bristle, 

 springing from a tubercle, seated upon one side of their base. They 

 are arranged in a single row upon the middle of each dorsal 

 segment, around the cornese of the middle pair of eyes, and on 

 the sides and anterior margin of the cephalo-thorax, presenting 

 the most acuminated form however in the first of these situations. 

 Upon the internal surface of the integument several rounded de- 

 pressions are seen to lead into the interior of these large tuber- 

 cles, showing that they are formed by simple eversions of the 

 epidermis, which has become hard and horny in such situations. 

 The smallest sized cells are continued for a short extent into these 

 cavities, which contain, generally, a blackish nodule of colouring 

 matter. The points of attachment of the muscular fasciculi are 

 apparent as numerous rounded or oval patches of a pale brown 

 colour, and of different sizes, placed upon slight internal eleva- 

 tions, which correspond with certain dark impressed punctaupon 

 the outer surface, and of a fibrous texture, resulting from the 

 still adherent but divided ends of the fasciculi. Internal to the 

 above layer is the second or pigmentary. It consists of a white, 

 delicate and homogeneous membrane which supports a granular 

 matter, disposed in patches between it and the epidermis, and 

 which corresponds in position with the dark spots and markings 

 seen upon the exterior of the animal, and is prolonged also into 

 the interior of the hollow tubercles. Beneath the above is a struc- 

 ture which may be regarded as analogous to the corium of in- 

 sects, yet which differs from it in not being composed of nume- 

 rous fibres interlacing with each other, but forming a single, 

 regularly disposed stratum or layer, similar to that found in the 

 Pulmonary Arachnida. It consists of several fasciculi, of large 

 size, and separated from each other by a considerable interval, 

 which are arranged longitudinally upon the under surface of the 

 animal, where they are also most numerous, but take a more or 

 less oblique direction upon the sides. They are composed of six 

 or more elongated and flattened fibres, lying close and parallel 



