220 Dr. David Sharp's Studies in Rhynchophora. 



" Aufsatz," while Niisslin prefers to call them the " acces- 

 sory parts." Attempts have been made to homologise 

 them, but sufficient is not known of their functions at 

 present. The part on which the functional orifice is 

 situate should be some guide, but this has hitherto been 

 too much neglected. As to the other " accessory parts " 

 little can be considered as settled. There are great differ- 

 ences in the inner structures of the tube in Scolytidae. 

 The subject has been discussed at length by both Verhoeff 

 and Niisslin in their considerations of Lindeman's views. 

 I can at present add nothing, though I may be permitted 

 to say that it is not clear that the sac functions in all the 

 groups in the same manner. As regards the variety in 

 the " acessory parts " of the Scolytidae reference may be 

 made to Lindeman's plates, and to Niisslin's discussion of 

 the point (Z. w. Insbiol., 1912, pp. 81-4). The necessity 

 of caution in homologising from simple inspection is evi- 

 dent from the fact that Niisslin considers the thirty-four 

 genera of Scolytidae found in Germany to belong to at 

 least twelve distinct subfamilies (loc. cit., p. 206). 



The Duct. 



This is another part that needs special investigation, 

 having been hitherto much neglected. It is sometimes 

 extremely long. Of course if a very long sac has to be 

 everted, there must be also a long duct, as this is carried 

 as far as the sac is extended. Usually the duct is very 

 easily seen, as it is surrounded by a very thick muscular 

 coating, but this disappears on maceration and the canal 

 is then fragile and difficult to detect. For the few par- 

 ticulars as to its course in Scolytidae refer to Niisslin (loc. 

 cit., p. 20). 



Methods. 



The means of making a rapid examination of these parts 

 are : have the insect to be dissected thoroughly penetrated 

 by water, keeping it at or near the boiling point for a minute 

 or two if small, for a quarter of an hour or more if large. 

 Take off the abdomen and place it in a strong solution of 

 caustic potash, having previously opened the abdomen at 

 one side, so that the macerating fluid shall enter in 

 readily everywhere. Leave it in the potash for a time 

 varying, according to the size and delicacy of the specimen, 

 from a few minutes to several hours. Take it out and put 



