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190 ME. A. D. lUCHAEL ON AN [Mar. 5, 



nuclei of about -01 mm. diameter, usually placed very regularly, 

 vvhich are best seeu in sections. The size and shape of the whole 

 gland varies a good deal in different individuals, and probably at 

 different times, but the average size may be considered to be about 

 •1 mm. by about -07 mm. Although this is the larger of the 

 two kidney-shaped salivary glands in Scbaub's species it is not so 

 in the present instance, the representatives of the other of the 

 two being somewhat larger. This latter pair of glands (figs. 16, 

 23, sgq.) cannot be called kidney-shaped in the present species, 

 each is more square with advancing rounded corners ; they are 

 not regular in shape, varying considerably in different individuals 

 &c., still they preserve their general form ; they are flattened dorso- 

 ventrally, and lie rather further back than the kidney-shaped pair ; 

 they are pressed against one another in the median line ; and their 

 posterior portions overhe and hide the anterior part of the brain, 

 when seen from the dorsal side. The average size of each of these 

 lands is about "11 mm. square. Simply for the sake of clearness 

 I will speak of them in this paper as the "quadrate salivary glands." 

 In spite of this general agreement in the form and position of 

 these two pairs of glands with those described by Schaub and 

 Croneberg, there is one leading point in which there is a very 

 marked difference from them, and indeed from all similar glands 

 vet described in the Acarina ; and that is, that all the authors 

 describe their glands, doubtless correctly, as discharging by a single 

 duct ; in the present species each of the four glands discharges 

 most distinctly by two paired ducts (dq., dr.) : whether this indi- 

 cates the original derivation of each gland from two which have 

 coalesced, I am not prepared to say ; they do not show any other 

 signs which I can detect of a double origin ; but the two ducts are 

 clear and unmistakable. In the kidney-shaped glands the ducts 

 spring from opposite sides of the gland a considerable distance 

 apart ; they are largest in diameter where they leave the gland 

 (about "01 mm.) and gradually diminish, their smallest part being 

 where they enter the main general duct (there they are about 

 •004 mm.) (tig. 16, di\). The two ducts from each quadrate 

 salivary gland (fig. 16, dq., fig. 21) spring from the underside of 

 the gland near its anterior edge ; they arise some small distance 

 apart, but considerably nearer together than those from the kidney- 

 shaped gland ; they are also much finer and more transparent than 

 those from the last-named gland, and enter the main general duct 

 together, joining just before they enter. They often overlie one 

 another ; thus while it is perfectly easy to see the two ducts from 

 the kidney-shaped glands, it requires very careful dissection to 

 demonstrate those from the quadrate glands ; one of these must 

 be dissected off, turned over to expose the under surface, and the 

 two ducts separated \\ith a very fine hair : if this trouble be taken 

 then the two ducts are perfectly apparent, and their whole course 

 may be traced to their entrance into the main general duct. I no\\- 

 come to the tubular salivary glands (fig. 16, sgt.)- these, although 

 essentially " tubular glands " are very different from, and much more 



