Taste — Muscles 49 



observation that insects are attracted by sweet or 

 by pungent substances, and experiments have proved 

 that they exercise selection in their feeding, guided 

 presumably by a sense of taste. In the Cockroach, 

 on the epipharynx, a number of pits have been 

 observed, containing nerve endings somewhat like 

 those just described as receiving smell sensations. 

 There can be no doubt that these are organs of taste, 

 and they are found in a similar situation in many 

 other insects. They have also been observed on 

 other parts connected with the mouth — on the inner 

 surfaces of the maxillae in Wasps for instance (fig. 33 

 E, F) and at the tip of the tongue in Ants, Bees, and 

 Flies (2, 27). 



Muscles. — The movements of insects, as of all 

 complex animals, are due to the action of special 

 bundles of contractile fibres called muscles. A 

 muscle may be readily split into fibres running length- 

 wise, and each fibre is as a rule surrounded by a 

 thin transparent sheath {sarcolemma), the space within 

 which is divided into compartments by a number of 

 membranes stretched across. Each compartment is 

 nearly filled by the true muscle-substance, forming 

 a contractile disc, made up of a bundle of numerous 

 many-sided fibrils. The series of transverse compart- 

 ments containing the muscle-substance gives an appear- 

 ance of cross-striation to the fibres when seen under 

 the microscope (fig. 44 a, m). Hence this muscle is 

 called " striped," and with very few exceptions all 

 the muscles of insects are of this type. In back- 

 boned animals, on the other hand, while the heart- 

 muscles and the muscles whose contractions cause 

 the voluntary movements of the body are striated, 

 those of the food-canal are unstriated — that is, the 

 fibres are made up of bundles of continuous fibrils 

 and are not cut into discs by transverse membranes. 



D 



