COCKROACHES 11 



emulsifying fat and rendering proteins soluble. 

 Thus the ordinary food substances are reduced 

 to a condition in which they are capable of 

 diffusing from the lumen of the alimentary 

 canal into the blood which floods the body 

 cavity. 



The external movement — one might al- 

 most say ' the panting ' — which is very 

 obvious in the abdomen, the alternate 

 flattening and deepening of this part of the 

 body, is a movement of inspiration and ex- 

 piration, the air being driven into the stigmata 

 and so into the tracheae or breathing- tubes. 

 There is a considerable variation in the rate 

 of these pulsations, but the cockroach's heart 

 beats at an average rate of seventy to eighty 

 contractions per minute. 



Although cockroaches have fairly developed 

 eyes, they seem to trust very largely to tactile 

 impressions in appreciating their relations to 

 the surrounding world. Their antennae and 

 the palps of their first and second maxillae 

 are constantly touching the surface on which 

 they are resting or moving, and from time to 

 time their antennae wildly wave in the air in 

 a manner which suggests that they are smelling 

 out the external circumstances which environ 

 them. The 39,000 sensory ' nerve-endings ' 

 which are found in the antennae of the male 

 cockroach are almost certainly olfactory in 



