It will be observed from what has been said that the head in these creatures is to a large extent the seat of the organs of sense and alimentation. What the function of the antennæ may be is somewhat doubtful, the opinion of scientific men being divided. The latest researches would indicate that these organs, which have been regarded as the organs of smell and sometimes as the organs of hearing, have probably a compound function, possibly enabling the creature to hear, certainly to smell, but also, perhaps, being the seat of impressions which are not strictly like any which we receive through our senses. [Illustration FIG. 34.--_Colias philodice_: _a_, antenna; _p_, extremity of palpus; _pl_, prothoracic leg; _ml_, mesothoracic leg; _hl_, metathoracic or hind leg; _t_, proboscis.] _Thorax._--The thorax is more or less oval in form, being somewhat flattened upon its upper surface. It is composed of three parts, or segments, closely united, which can only be distinguished from one another by a careful dissection. The anterior segment is known as the prothorax, the middle segment as the mesothorax, and the after segment as the metathorax. The legs are attached in pairs to these three subdivisions of the thorax, the anterior pair being therefore sometimes spoken of as the prothoracic legs, the second pair as the mesothoracic legs, and the latter pair as the metathoracic legs (Fig. 34). On either side of the mesothorax are attached the anterior pair of wings, over which, at their insertion into the body, are the _tegulæ_, or lappets; on either side of the metathorax are the posterior pair of wings. It will be seen from what has been said that the thorax bears the organs of locomotion. The under side of the thorax is frequently spoken of by writers, in describing butterflies, as the _pectus_, or breast. _The Abdomen._--The abdomen is formed normally of nine segments, and in most butterflies is shorter than the hind wings. On the last segment there are various appendages, which are mainly sexual in their nature. [Illustration FIG. 35.--Leg of butterfly: _c_, coxa; _tr_, trochanter; _f_, femur; _t_, tibia; _tar_, tarsi.] _The Legs._--Butterflies have six legs, arranged in three pairs, as we have already seen. Each leg consists of five parts, the first of which, nearest the body, is called the _coxa_, with which articulates a ring-like piece known as the _trochanter_. To this is attached the _femur_, and united with the femur, forming an angle with it, is the _tibia_. To the tibia is attached the _tarsus_, or foot, the last segment of which bears the claws, which are often very minute and blunt in the butterflies, though in moths they are sometimes strongly hooked. The tibiæ are often armed with spines. In some groups of butterflies the anterior pair of legs is aborted, or dwarfed, either in one or both sexes, a fact which is useful in determining the location of species in their systematic order.