1NSECTA. 



935 



those of the larger animals in not being in- 

 closed by aponeuroses, and in being formed of 

 fibres which are always free, straight, and fre- 

 quently are not connected with or arise from 

 tendons. There is no instance, as Straus has 

 correctly remarked, of a digastric muscle in 

 insects. Each fibre is composed of a great 

 number of very minute fibrillae, or fasciculi of 

 fibrillae, into which the fibre may be easily 

 torn, after it has been hardened for some time 

 in spirits of wine. Professor Wagner has seen 

 transverse striae on the fibres of insects as on 

 those of vertebrated animals, and we have 

 also observed them very distinctly on the dorsal 

 longitudinal fibres of Lucanus cervus, and 

 more particularly on the fibres of the longitu- 

 dinal muscles of the back, in the abdominal 

 segments of the larva of Odonestis potatoria ; 

 Professor Muller states that the voluntary mus- 

 cles of insects are wholly constituted by these 

 transversely striated fibres, each of which has 

 a very delicate sheath, which can often be per- 

 ceived forming a transparent border to the 

 fibre.* Those fibres which are entirely with- 

 out tendons are attached by their whole breadth 

 either directly to the flat internal surface of the 

 dermo-skeleton or to elevated ridges, which are 

 intussuscepted portions of the tegument within 

 the body, the apodemata of Audouin, of which 

 the phragmata before described are examples. 

 The tendons, or hard uncontractile ends of the 

 muscles, like the phragmata, are formed by an 

 elongation inwards of parts of the internal 

 lamina of the dermo-skeleton .f They exist 

 more generally in the perfect insect than in the 

 larva, and in the muscles of the head of the 

 larva than in other parts of the body. The 

 cause of this appears explicable by the fact that 

 there is a higher developed condition of body 

 in the perfect insect than in the larva, and in 

 the head of the latter than in other parts of its 

 body. Distinct tendons exist most frequently 

 in the muscles of the extremities and organs 

 of manducation, as in the Lucanus cervus 

 (fig- 388, 2), in which a large flat tendon, of 

 great strength, is attached to the external con- 

 dyle of the mandible, and on each side of 

 which the fibres that compose the great ex- 

 tensor penniform muscle are inserted. Tendons 

 exist also of great length in the legs of Orthop- 

 tera (fig. 409, , b, c), and between the forked 

 processes of the thoracic segments, and the 

 margins of the coxae. The muscles with ten- 

 dons are arranged by Straus under two divi- 

 sions : I first, the conical, in which the tendon 

 is short and occupies the axis of the muscle, 

 where it is expanded into a broad plate, unto 

 which the fibres of the muscle, originating 

 from a broad base, and converging to one point, 

 are attached, and the tendon then proceeds 

 alone to the point of insertion ; second, the 

 pyramidal, in which the tendon, as in the 

 conical, is surrounded by short fibres, and is 



* Elements of Physiology, (translation,) partiv. 

 p. 882. 

 t Straus. 

 $ Op. cit. p. 146. 



broad and divided into several laminae ; third, 

 the pseudo-penniform, in which the fibres ori- 

 ginate in a row, and, converging, are attached 

 sometimes on one side, and sometimes on both 

 sides of a long narrow tendon ; fourth, the 

 penniform, which differ from the last in the 

 margin of the tendon being fibrous. Like the 

 latter the fibres originate sometimes on one 

 side only, and sometimes on both. Fifth, the 

 compound, or those which consist of several 

 muscles, each formed of two or more fibres, 

 united by a tendon, and these tendons of two 

 or more muscles united into one bundle ; or 

 in which the tendons of several bundles of 

 muscles are united. Unto these five forms 

 Burmeister has added a sixth, the cylindrical,* 

 the tendon of which is a flat round plate, to 

 which the fibres are attached on one side, and 

 from which a process extends on the opposite 

 to the point of insertion, as in the muscles of 

 the wings. Audouin calls these tendons epi- 

 dcmes, and regards them as processes of the 

 thorax. 



The muscles of the larva present great uni- 

 formity of size and distribution in every seg- 

 ment, the motions of each of these divisions 

 of the body being almost precisely similar. 

 The differences which exist in the number, dis- 

 tribution, and functions of the muscles, are to 

 be sought for in the first four segments, which 

 compose the head and thorax of the perfect 

 insect. Thus, in the head of the larva there 

 is a greater aggregation of muscles than in any 

 other segment of its body, because a greater 

 number of organs exist, and consequently 

 require these additional muscles. The pre- 

 sence of a greater number of organs in this 

 than in the succeeding segments is readily ac- 

 counted for, when we remember that the head 

 is composed of several sub-segments, and that 

 the appendages belonging to it are those of 

 these originally distinct parts. But the situ- 

 ations and the form of the muscles have become 

 changed from those of the simple muscles of a 

 segment, and some have become united to 

 others. This may explain the cause of the 

 greater complexity of the muscles of the head 

 of the larva than of those of the other seg- 

 ments, and why so few are simple like those 

 of the abdominal regions, but, on the other 

 hand, are frequently complicated, and end in 

 tendons, and more or less resemble in form 

 the muscles of Vertebrata. Hence the muscles 

 of the mandibles are large and occupy the 

 greater part of the lateral and posterior region 

 of the cranium, the extensor muscles being 

 attached to the lateral and posterior surface of 

 the cavity, like the extensor muscles of the 

 legs in the thoracic segments, and the flexor 

 more internally to parts that correspond to the 

 lamina squamosa in the head of the perfect 

 insect, the analogies of which in the thoracic 

 segments are the forked processes to which 

 the flexor muscles of the legs are attached, 

 like the corresponding muscles of the man- 

 dibles on the head. The muscles of the three 



* Manual of Entomology, (trans.) p. 24y. 



