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Show 1895.] HYDEACHNID POUND IN COENWALL. 189 of salivary glands very similar to Croneberg's-two pairs which he calls kidney-shaped, and one which, following Croneberg, he properly calls pipe-shaped or tubular (schlauchformig); this gland he says has its blind end fixed to a chitinous projecting piece or band arising from the anterior edge of the body near the side of the rostrum, and about the level of the top of the brain; the gland then runs nearly straight backward until it reaches a point about one-third of the length of the body (without rostrum) from the anterior edge of the body; the gland then makes several twists on itself, running across the body toward the median line, but not reaching it; then runs forward again, soon loses its twisted character, and approaches its point of origin, thus forming a nearly complete loop, and ends in a long fine duct running toward the mouth. Schaub was not able to trace this duct to its point of discharge, nor was he able to determine with certainty whether the two kidney-shaped glands and the tubular gland on each side join in a common efferent duct, as Croneberg says, or not; but he says that if they do, in his species, the juncture must be very near the mouth, as he has traced the three separate ducts a long way; he seems to m e to doubt their joining at all. Croneberg describes a tubular salivary gland in Trombidium with a course very similiar to that given by Schaub]; and Pagenstecher had described it in 1860. In the present species there is a very decided resemblance to the condition described by Croneberg and Schaub; the general scheme of the salivary organs is undoubtedly homologous, but the whole thing is more elaborated and the differences in detail are numerous and of some importance; on the whole, Croneberg's species and description come nearer to Thyas petrophilus than Schaub's do. In the species which I a m describing there are at least three pairs of salivary glands (I will explain later on w h y I use the expression " at least"), two of these are clearly the homo-logues of the kidney-shaped glands and one of the tubular gland. If the creature be opened on the dorsal surface, and tbe dorsum and fat-body and other surrounding organs be removed, it will be found that just anterior to, and a little to the side of, the brain is a gland which may fairly be described as reniform (fig. 16, sgr.); it represents the " larger dorsal mouth-gland " of Schaub, wiiich it greatly resembles in general appearance; a very similar gland w^as described as long ago as 1860 by Pagenstecher (in Trombidium), although his details may not be quite correct, and in 1861 by Gudden in reference to the Tyroglyphidae2. This gland in Thyas petrophilus is formed of large secreting-cells radiating almost from a centre: these cells have an exterior measurement of about •02 mm., and a length, measuring from the exterior toward the centre, of about #08mm.; tbey have large, very clearly-marked 1 " Ueber den Bau von Trombidium," Bull. Soc. Imp. d. Nat. de Moscou, 1879. 2 " Beitrag zur Lehre von der Scabies," Wiirzburger medicinische Zeitsch. 1861, p. 301, and zweite vermehrte Auflage, Wurzburg, 1863. |
