SCIENCE- G OS SI P. 



position on ceilings and glass. Here we meet with 

 a difficulty ; if the hairs are not hollow, and there 

 are no openings in the lower wall near them, how 

 •does the viscid fluid get on to them ? It has 

 occurred to me that bej'ond the above-mentioned 

 function the viscid fluid may fulfil a much higher 

 purpose to man and other animals. In flies which 

 deposit their eggs, but do not feed upon decom- 

 posing and often diseased animal matter, the fluid 

 would entomb any disease germs taken up by their 

 feet. This, of course, is supposing that the fluid 

 hardens on exposure to the air, like the fluid 

 emitted by the spinnerets of spiders and the larvae 

 of some Lepidoptera. I do not wish to imply that 

 flies do not in any case disseminate disease germs. 

 This, I believe, is commonly done when they feed 

 on fluids containing such germs. 



Hilara pilosa. Longitudinal Sections of the Tarsus 

 ■of the Male (fig. 2). — In the male insect the first 

 Joint of the tarsus is greatly enlarged. In section, 

 the most prominent feature is the numerous large 

 glands with their ducts ; the apodeme, the nerve, 

 and tracheae are also shown, whilst no muscle is 

 visible. The ducts penetrate the inner wall of the 

 joint, and the outlet can be seen in one of the sec- 

 tions immediatelybehind a large hair. The pur- 

 pose of the secretion from these glands in all 



Fig. 2. First Joixt of Taiiscs of Hilara pilosa. 



^probability is the same as those in water-beetles, 

 where the glands have their outlets in both the 

 large and small discs on the anterior feet. 



Sections of Head of Blow- fly (figs. 3 and I). — 

 'These commence with the first section at the back 

 of the head and continue the series. From the 

 .amount of loose embryonic cells seen in the sections 

 it is evident that this fly had recently emerged 

 from the pupa-case. On one slide there are 

 numerous sections of the brain and optic tract ; 

 -and as they are fairly thin, about J^ mm., most of 

 the recent discoveries may be compared with 

 them. M. N. Newton, "Mag: Nat. Hist.," 1879, 

 p. 397, states that " in the cerebroid or supra- 

 • oesophageal ganglia are situated the organs of 

 the perception of memory, of intelligence, etc. 

 Hence they have a more complicated histolo ical 

 structure than the suboesophageal ganglia, which 

 principally govern the appendages of the mouth. 

 These nerve-centres are nevertheless constructed 

 •on the same general plan as the other ganglia. In 

 the middle they present bundles of nerve-fibres, 

 while the nerve-cells principally occupy the 

 periphery." In these sections nerve-fibres may be 

 traced from the centre of the oesophageal ganglion 

 to well-defined peripheral nerve-cells. There is 

 here a likeness to the vertebrata, though in almost 

 •every other respect we find the opposite, except- 

 ing the muscles and nerves. The compound eye 

 and optic nerve have been so ably worked out by 

 Hickson that I need only refer to his paper in the 

 •quarterly " Journal of Microscopy," No. XCVIII. 

 'The ocelli or simple eyes are well seen in these 



sections. There are also several sections through 

 the frontal sac. Lowne believed this to be an 

 olfactory organ adapted to the appreciation of 

 powerful odours. If we look at the head of the 

 insect as an almost closed sac bounded by rigid walls, 

 with all otherwise unoccupied spaces filled with a 



\--^ 



Fig. 3. Head of Blow-fly. 



circulating fluid (the blood) whose communication 

 with the thorax is by a very small neck and that 

 small space partially taken up by the oesophagus, 

 nerve-chords, and tracheae, it is evident that 

 the blood could not pass so quickly into or 

 out of the head as would admit of the quick 

 protrusion or retraction of the proboscis. Hence 

 in the frontal sac there is a beautifully 

 simple contrivance well adapted for such a 

 purpose. It is a simple sac suspended near the 

 upper wall of the head with the under surface 

 hanging in numerous folds. The sac is in free 

 communication with the outer air through an 

 opening in the forehead immediately above the 

 antennae. The outer surface is covered with 

 numerous papillae ; when the folds are brought so 

 close together that the papillae interlock they 

 always enclose some air, thus preventing any 

 adhesion of the surfaces, which might be the case 



Fig. 4. Head of Blow-fly. 



if the surfaces were smooth and moi.st. By this 

 means an equable pressure is maintained on the 

 brain and other organs. Some four or five years 

 since I read a paper before the members of the 

 Sheffield Microscopical Society on the frontal 

 sac, which was afterwards published in SciENCE- 

 GossiP. There are sections also of the antennae. 

 They are mostly cut through the second and third 

 joints, the first not being in the same plane. 

 Exteriorly the head is covered with two kinds of 

 pigmented hairs ; the finer and smaller appear to 

 be nothing more than clothing, but the larger ones 

 are hollow, their lumen continuing through the 

 chitinous wall of the joint. The interior of the 

 joint is lined with epithelium, the ends of the 

 cells being drawn out and projecting into the lumen 

 of the hairs. This is distinctlv shown in thin 



