STRUCTURE OF THE MYRIOPODA. 151 



limbs in insects, the first three will be the coxa, trochanter, and femur, the fourth and fifth will 

 represent the tibia, as in the Spiders, and the sixth, or sixth and seventh, which usually differ more or 

 less in form from the preceding ones, will form the tarsus. 



In their internal structure the Myriopoda closely agree with the insect type. The intestinal 

 canal shows the same parts as in the Insecta, but usually drawn out to a greater length, to correspond 

 with the general elongation of the body, through which it passes nearly in a straight line. A narrow 

 oesophagus gradually expands into a stomach, which, however, is only a widened part of the tube, and 

 this is followed by a straight intestine running to the extremity of the body. As appendages to the 

 intestinal canal, we find from one to three pairs of salivary glands, and one or two pairs of 

 Malpighian vessels, the former opening into the cavity of the mouth, the latter into the intestine not 

 far from its termination. The nervous system of these animals consists of a ventral chain, which 

 shows the same uniformity of general construction that is observed in the larvje of insects with a 

 perfect metamorphosis, the ganglia corresponding in number with the body-segments, except that in 

 most cases the commissures uniting the successive ganglia are very short, often so short that the 

 central system forms a cord rather than a chain. The ganglia of the first three segments following 

 the head are regularly united into a continuous mass. In the head there is the same nervous ring 

 embracing the oesophagus as in insects, and from it are given off nerves to the antenna? and eyes, the 

 latter of considerable thickness when the organs of vision are greatly developed. In the worm-like genus 

 Peripatus, which is placed with the Myriopoda, but in all probability represents a survival of a type 

 intermediate between the Annelida and the Myriopoda, the ventral nervous cords are widely separated. 



As in the Insecta, the central organ of circulation, the so-called heart, is a dorsal vessel, divided 

 into successive chambers agreeing in number with the segments of which the body is composed, and 

 each chamber is attached to the walls of its segment by a pair of triangular muscles. The blood 

 penetrates these chambers through a pair of lateral slits, and, according to Newport, a portion of it 

 is again driven out through a small artery situated in front of the slit, but the greater part is driven 

 forward and discharged into the cavity of the head through an aorta which divides into three 

 branches. Respiration, as already stated, is effected, as in the Insecta, by the agency of trachea}, 

 which open by regular stigmata, usually placed either towards the middle of the ventral surface close 

 to the articulations of the legs, or in the membrane uniting the dorsal and ventral plates of the 

 segments. In one type, however, the stigmata form a single row of openings in the middle of the 

 upper surface of the body, one being placed close to the hinder margin of each of the dorsal plates; 

 and in Peripatns the trachea? are short and open irregularly in all parts of the skin of the animal. 



The reproduction of the Myriopoda is always by eggs, and the young animals, on quitting the 

 egg, although allowing the general characters of their parents to be recognised, present certain rather 

 important differences from them. Thus the numbers of the body-segments, of the joints in the 

 antenna? and of the ocelli are always less, and the young Myriopod, when first hatched, has only 

 three pairs of legs attached to the three segments immediately behind the head. With each change of 

 skin undergone by the larva the number of each of these parts increases until the adult construction is 

 attained ; new segments are formed in the body between those already in existence, new joints are 

 added to the antenna? in the same way, new ocelli make their appearance on the sides of the head, 

 and the number of leg-bearing segments steadily increases. 



In their habits the Myriopoda are generally darkling creatures, living a concealed life in the 

 ground, under stones, in crevices of rocks and buildings, and under the loosened bark of trees. They 

 are distributed in all parts of the world, but the largest and finest species are all inhabitants of hot, 

 climates, where some of them attain gigantic dimensions. The food of some of them is of a vegetable 

 nature, although it would appear that even these will not disdain animal food 011 occasions ; others 

 confine themselves to the latter diet, and are most formidable predaceous creatures. 



The oldest known members of the class, in fact almost the only ones known to occur in the fossil 

 state, belong to the vegetarian forms above mentioned (the Chilognatha). Remains of several species 

 apparently belonging to this order, although showing very peculiar characters, have been discovered in 

 the Carboniferous formation of North America, some of them even contained in the ho' low trunks of 

 trees of the genus Sigillaria. One or two allied forms have also been detected in the Coal Measures 

 of Britain. The Permian rocks of Germany, immediately succeeding, or, perhaps, concluding the 



