10 ENTOMOLOGICAL SOCIETY 



was mimicked must be distasteful. He also mentioned 

 another which closely resembled bird droppings, the liquid 

 portions being represented by the web. 



Mr. Banks identified the last mentioned as Philodromus 

 ornatits Bks., and stated in addition that, so far as he knew, 

 none of the spiders was actually distasteful to its enemies. 



— Doctor Stiles then addressed the Society on the subject 

 of the stigmal plates of the genus Dermacentor, illustrating 

 his talk by a series of fine drawings. He spoke of the diffi- 

 culty of separating the species of this genus by means of the 

 characters which have usually been employed for this pur- 

 pose, and of his discovery that the microscopic structure of 

 the stigmal plates show definite characters that can be de- 

 pended on when all others fail. These characters are of 

 a nature that they may be studied to advantage only by means 

 of the compound microscope, and consist principally of the 

 number and arrangement of certain goblet-shaped cells, the 

 exact function of which in the economy of the animal he had 

 not been able to determine. Each species of the genus was 

 taken up in turn, mention of previous confusion in its de- 

 termination was made, and the shape and character of the 

 stigmal plate illustrated by means of drawings. While there 

 is considerable individual variation in the plates from dif- 

 ferent specimens within a species, there are certain char- 

 acters which can always be depended upon, and by means 

 of these he had for the first time been able to determine the 

 species of the genus to his continued satisfaction. 



Considerable discussion followed, largely concerning the 

 relative value of the stigmal plates and other characters for 

 the determination of the species. In the course of this Doctor 

 Stiles reaffirmed that his studies, which were based on the 

 careful examination of hundreds of mounts, had fully con- 

 vinced him that in many cases valid determinations of these 

 ticks are impossible unless the stigmal plates are taken into 

 consideration. He stated that in genera other than Derma- 

 centor they appear to be of some value, but to what extent he 

 had not determined. He described the technique by which 

 the results were obtained. Mr. Banks stated that the shape 



