1895.] HYDEACHNID POIWD 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 (schlauchfdrmig) ; 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 tv^•ists 

 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 me to doubt their joining at all. Croneberg 

 describes a tubular salivary gland in Tromhidium 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 petropliihis than 

 Schaub's do. In the species which I am describing there are at 

 least three pairs of salivary glands (I will explain later on why I 

 use the expression " at least "), two of these are clearly the homo- 

 logues of the kidnej'-shaped glands and one of the tubular gland. 

 If the creature be opened on the dorsal surface, and the 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, sr/r.) ; it 

 represents the " larger dorsal mouth-gland " of Schaub, which it 

 greatly resembles in general appearance ; a very similar gland was 

 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 Tyroglyphidse ^. This gland in Thyas 

 petropMlus is formed of large seereting-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 '08 mm. ; they have large, very clearly-marked 



^ "TJeber den Bau von Trombidium," BuU. Soc. Imp. d, Nat. de Moscou, 

 1879. 



^ " Beitrag zur Lehre von der Scabies," Wurzbui-ger medicinische Zeitsch. 

 1861, p. 301, and zweite vermehrte Auflage, Wurzburg, 1863. 



