A pair of limbs to each segment. Antennae branched. Eyes few or none. Labrum and labium indistinct. Genital orifice at the base of the second pair of limbs. Free dorsal scutes. Nine pairs of feet (always?). Some segments with sensitive hairs. Last segment the smallest.
Family 1. Pauropidae.
Body slender. Dorsal scutes smooth. Limbs long and projecting from the lateral margins of the body. Colour pale.
The Structure of the Myriapoda.
Having now given a short view of the classification of the Class, I will proceed to give a general account of their structure, the variations in which have led to the divisions into the various Orders and Families. Their structure shows resemblances to several widely different classes of animals. One cannot help being impressed with their likeness to the Worms, at the same time they have affinities with the Crustaceans, and still more with the Insects. In the latter class the likeness of the Thysanuridae to Scolopendrella and Pauropus have induced a celebrated Italian anatomist, Professor Grassi, to claim the former as the ancestors of the Myriapoda.
Myriapods have a body which is segmented, as it is termed; that is, composed of a number of more or less similar parts or segments joined together.
One of the most important characteristics which distinguish Myriapods from other Arthropoda is the fact that they possess on the posterior segments of the body true legs which are jointed and take part in locomotion. The head is in all cases quite distinct from the body, and may be regarded as a number of segments fused together into one mass. Their heads are always provided with a single pair of antennae and mouth appendages, consisting of an upper lip, a pair of mandibles or jaws, and one to two pairs of maxillae. The mandibles resemble those of Insects, and are strongly toothed. In the Chilognatha a pair of maxillae are fused so as to form a single oval appendage. In the Chilopoda they each consist of a single blade bearing a short palp or feeler. The mouth parts may have the forms known as chewing, biting, or suctorial (Polyzonium) mouth appendages.
With the exception of the terminal segment, and in many cases the first or the seventh, each segment bears one or two pairs of limbs. These may be very long, as in Scutigera, or very short, as in Polyxenus. They may be attached close to one another near the ventral middle line of the body, or may have their bases far apart from each other, as in the Chilopoda. The exoskeleton or external armour is composed of chitin (Chilopoda) or of chitin with calcareous salts deposited in it (Chilognatha).
Their internal structure has a great likeness to that of Insects.
The general position of the internal organs may be seen from Fig. 28, which shows a Lithobius dissected so as to exhibit the digestive and nervous systems.