| OCR Text |
Show 1893.] ACARUS FOUND IN CORNWALL. 265 LENTUNGULA ALGIYORANS. (Plate XVIII.) Average length without mandible about "38 mm. Greatest breadth about *20 m m . Length of legs 1st pair about -13 m m . „ „ 2nd „ „ -14 m m . ,, „ 3rd „ „ '15 m m . „ 4th „ „ -15 m m . Colour.-The actual colour of the creature, if it had been fasting for a long time, would probably be almost entirely light yellowish, but as ordinarily seen it is dark olive-brown with very numerous light yellowish spots and markings. The yellowish colour is chiefly in spots and spaces surrounded with the olive, but the spots are not arranged in any definite pattern; although a few spots on the cephalothorax have a tendency to be permanent, the whole of the markings are most irregular and varying. The olive-brown colour greatly predominates, and some specimens are almost wholly of that tint. The colour apparently arises from the diffusion of food material or products, it is not pigment in the cuticle; this can be demonstrated by placing a dark specimen in a drop of water on a glass slip under the microscope and placing a cover-glass over it; as the water evaporates the cover will be slowly drawn down, producing pressure upon the creature ; the result of this will be that what appears like the whole contents of the body are gradually discharged from the anus, and the opaque dark creature becomes yellowish white and transparent. During life the brown colour does not, however, look like food-contents, it has every appearance of being the true colour of the greater part of the body. The rostrum and legs are always pale pinkish yellow. Texture polished. Shape.-This also depends considerably upon whether the creature is fully fed; when it is so the distinctive form is lost, and the Acarus becomes almost a roll with little shape in it, but when not quite so fully fed the form is rather striking. The cephalothorax is slightly broader than the abdomen, but much thinner dorso-ventrally, so that where the two join the dorsum of the abdomen stands high above the cephalothorax. There is a sharp indentation in the lateral edge of the creature, where cephalothorax and abdomen join; behind this the abdomen of the female is almost sack-shaped ; that of the male narrows a little more posteriorly ; in both sexes the hind margin is indented in the middle, so that each side forms a rounded lobe. Cephalothorax.-The rostrum is a smooth tube or collar, long for the family; the strong chelate mandibles project considerably; each arm of the chela is tridentate (fig. 7). The five-jointed palpi (fig. 8), of the ordinary type, are adherent to the membranous maxdlary lip, in the centre of and below which is a chitinous triangular sclerite which might possibly be considered to represent a labium. The central portion of the cephalothorax, behind the rostral tube, forms a large, rounded, fleshy lobe which overhangs the |
