182 SELECTED NOTES. 



insect, as he says the facial plate is caused to vibrate rapidly during 

 the emission of sound, which in the apparent absence of sufficient 

 muscular power it is difficult to conceive. 



The last is that it is an olfactory organ, though with a limited 

 nerve supply, by means of which the creature is enabled to appre- 

 ciate powerful odours. Mr. Jenkinson's last suggestion — viz., the 

 function of the laterally opening tracheae in the interior of the 

 body by means of capillary vessels — or something analogous — it 

 seems to me, will be very difficult to establish ; and if so, the 

 advantage of such connection would appear doubtful owing to the 

 extreme minuteness of such capillaries did they exist, for any 

 exchange of air in the tracheae which is effected by the respiratory 

 movements of the abdomen could hardly proceed more rapidly 

 one way than the other. E. Bostock. 



Hairs on the Pulvilli.— I quite agree with Mr. Bostock that 

 the hairs beneath the pulvilli may act mechanically in helping to 

 relieve the foot. My difficulty is simply this : — If the glands in 

 the pulvillus secrete a viscid fluid, how is that fluid conveyed to the 

 under-surface of the pulvillus ? When I approached the subject, 

 I expected to find a lumen in each hair, or, failing that, minute 

 ducts passing through the external wall, but I can find neither. 



The Frontal Sac is continuous with, and is simply an invagina- 

 tion of the epidermis. It is a flexible bag, floating in and sur- 

 rounded by fluid, and in my opinion is unsuitable for producing 

 quick vibrations, but would rather tend to subdue them ; hence, I 

 think, we must look somewhere else for the "humming" organ. 

 It is equally unsuitable for an olfactory organ, because its only 

 nerve-supply could be obtained by its outer edges, and these would 

 be very limited, even if they exist at all, which is extremely 

 doubtful. 



The experiment of placing the thorax of a cricket under 

 water, while the abdomen had free access to the air, showed 

 bubbles of air emitted from the thoracic spiracles, without the 

 insect being in the least exhausted. When the abdomen was 

 immersed no bubbles were emitted, and the insect suffered from 

 exhaustion. Such, experiments, coupled with the construction of 

 the thoracic spiracles, suggest that they are outlets for the expired 



