\\ \IM\IS \\|, PHI 101 



thi- doe- n<>t prove t h;it tin- * i>|. 



though ii .\v lh;il llu-y BTC not the loic attraction- ' 



an important L'uide. I he honey bcC !-> able to di\t: color 



pattens, aeenrding to the experiment II. TIM-MIT. 



Problematical Sense Organs. As all our id. -./.-ml t< 



-motions of Insectfl arc necessarily inlVn-m > from OW -y ex- 



periences, they arc inevitably inadequate. While it i : that in- 



bave at least the BenSCfl <>f touch inell. hearin. -lit. it 



is also certain that these senses 'f theirs di irkably in ran^e from 



our own, as we have shown. We can form no accurate conception of 

 ordinary senses in insects, to say nothing of otht r- that insects 

 have, some of which are probably peculiar to insects. Thus they have 

 many curious integumentary organs which from their structure and 

 nerve connections are inferred to be sensory end-organs, though their 

 functions are either doubtful or unknown. Such an organ is the sensil- 

 lum placodeum (p. 84), the use of which is very doubtful, though the 

 or^aii is possibly affected by air pressure. Insects are extremely sensi- 

 tive to variations of wind, temperature, moisture and atmospheric 

 ure. and very likely have special end-organs for the perception of 

 these variations; indeed, the sensilla trichodea are probably affected 

 by the wind, as we have said. 



The halteres of Diptera, representing the hind wings, contain sensory 

 organs of some sort. They have been variously regarded as olfactory 

 (Lee), auditory (Graber), and as organs of equilibration. When one or 

 both halteres are removed, the fly can no longer maintain its equilibrium 

 in the air, and Weinland holds that the direction of flight is affected by 

 the movements of these "balancers." 



6. DIGESTIVE SYSTEM 



The alimentary tract in its simplest form is to be seen in Thysanura, 

 Collembola and most larva-, in which (Fig. 146) it is a simple tube ex- 



,-py 



-Alimentary tract of a collembolan, Orchestlla. F. fore gut; H, hind gut; J/, 



mid gut; c. cardiac v.i Im, longitudinal muscle; 



ve. 



