SELECTED NOTES. 181 



I desire to express my great pleasure in the examination of 

 Mr. Jenkinson's beautifully mounted slides, and in the perusal of 

 his interesting and instructive notes, as well as my satisfaction in 

 seeing the work of so earnest and careful a worker circulating 

 among our members. 



Hairs on the Pulvilli of Flies.— With regard to the difficulty 

 respecting the hairs on the pulvilli of flies, is it to be expected that 

 the hairs should be hollow, and in the nature of ducts for the 

 viscid fluid secreted by the glands ? Do they — the hairs — not act 

 rather as a simple mechanical method for enabling the insect 

 instantaneously to detach its foothold from the object upon which 

 it has been resting ? and supposing the pulvillus to be hairless, and 

 the secreting surface to be brought into close connection with the 

 object, would there not be great difficulty in the creature at once 

 liberating itself? 



Frontal Sac— The function of the frontal sac is a very inter- 

 esting subject, and I am inclined to agree with Mr. Jenkinson that 

 it acts largely as a compensatory arrangement in the adjustment of 

 the pressure upon the organs of the head, in which the protrusion 

 of the proboscis and its retraction must otherwise occasion con- 

 siderable variation, but at the same time it doubtless fulfils other 

 purposes. 



I have not yet seen Prof. Lownes' new edition of his work on 

 the Blow-fly, in which, however, I believe he has in several ways 

 considerably modified his views on certain points communicated 

 in his first edition ; and do not know whether the views he held 

 upon the frontal sac are in any way altered, but I think he there 

 ascribed several functions thereto. The first of these was that this 

 sac effected the purpose of a lever to enable the maturing imago 

 to escape from the pupal case by forcing off" the upper end and so 

 permitting the insect to escape. At this time the frontal sac, 

 which forms a cavity in the head of the mature fly, is everted, and 

 forms a protuberance in front of the head, which, however, imme- 

 diately after convergence, collapses and is withdrawn into the head, 

 from which, by a slight pressure, it can be again made for a short 

 time only to protrude. 



The second function is in connection with the humming of the 



International Journal of Microscopy and Natural Science. 

 Third Series. Vol. VII. n 



