NO. lO MORPHOLOGY OF GNATHOTRICHUS SCHEDL 67 



(d) Abdachungszaehne (Nuesslin), masticatory teeth which have 

 two dentations, one, the totahty of all composing the mastica- 

 tory brush, and a second smaller tooth on the instep, the 

 totality of which forms a second brush consisting of a single 

 row of teeth only. 



In the classification of the Scolytidae based on the proventriculus, 

 Gnathotrichus should be placed with Xyhtcrus Er., Xylcborus Eichh., 

 Anisandrus Ferr. and other ambrosia beetles together in one group. 

 There is little doubt that the similarity of the digestive systems in 

 ambrosia beetles of the Supcrfamily Scolytoidca is of no importance in 

 the classification. These are merely parallel modifications of groups 

 deriving from very different ancestors. 



The proventriculus is very similar in all three species of Gnathotri- 

 chus and it is not possible to distinguish them by characters of this 

 part. 



Mid-intcstinc. — -The mid-intestine is about one-third of the whole 

 length of the alimentary canal. According to Nuesslin the proportions 

 are the same as in Anisandrus dispar Fabr. and Xyloierus lincatus 

 Oliv. 



In Gnathotrichus two subdivisions of the mid-intestines are well 

 defined. The anterior part, which presents the widest part of the whole 

 alimentary canal, has the form of a ball and is covered with short, 

 half spherical gastric coeca. This part is here designated as the ven- 

 triculus proper. The posterior, much narrower tubelike part, is here 

 called the posterior tube of the mid-intestine. It bears much smaller 

 gastric coeca which distinctly decrease in size toward the origin of 

 the Malpighian vessels and which are always more filiform in shape. 

 The origin of the Malpighian vessels marks the posterior limit of the 

 mid-intestine. These are rather narrow, long tubelike vessels, strongly 

 entangled around the posterior part of the mid-intestine and do not 

 vary noticeably in size. 



Hind-intestine. — While the fore- and mid-intestine are situated as 

 a straight tube in the body, the hind intestine forms a distinct loop. 

 The latter does not bear any gastric coeca but is characterized by the 

 muscles which enclose it. The subdivisions, the small and large in- 

 testine and the rectum, are not so clearly separated. The ovaries of 

 the female reproductive organs are always situated above the hind 

 intestine ; the testi of the male lie under and ventral to it. 



The Larvae 



On account of the difficulty in getting material of the western 

 species, the following discussion is based on Gnathotrichus materiaritis 

 Fitch only. 



