STRUCTURE OF CHILOGNATHA 



53 



The next appendages to be mentioned are the mouth parts. 

 These differ in form from those of the other Orders, and their 

 differences are connected very largely with the fact that the 

 Chilognatha live on vegetable substances. Their mouth parts 

 are adapted for chewing, except in the case of the Polyzoniidae, 

 the eighth family of the Order, in which, according to Brandt, 

 the mouth parts are adapted for sucking, and are prolonged 

 into a kind of proboscis. The mouth parts of the Chilognatha 

 consist of 



(1) An upper lip. A transversely-placed plate, which is fused 



with the rest of the head. 



(2) A pair of powerful mandibles or jaws adapted for mastica- 



tion, and moved by powerful 

 . muscles. / and g in Fig. 33 

 shows these mandibles, while 

 the rest of the figure consti- 

 tutes the broad plate (No. 3). 



(3) A broad plate covering the under 



part of the head and partially 

 enclosing the mouth. This Fig. 



Myriapoden. ) f and g. 

 The mandibles. The parts 

 marked a, h, c, d, e are 

 firmly united and consti- 

 tute the broad plate No. 3. 

 They have received the 

 following names a, b, In- 

 ternal stipes ; c, external 

 stipes ; d, malellae ; e, 

 hypostoma. 



33. Mouth parts of 

 , , , . , in OhilognatJm. (From C. L. 



Structure, which, as we shall Koch, Die System der 



afterwards see, is formed by 



the fusion of two appendages 



which are distinct in the 



animal when just hatched, has 



been called the deutomalae, 



the jaws receiving the name of 



protomalae. 



After the mouth parts we come to the legs. "We first notice 

 the fact that the bases of the legs in each pair are closely 

 approached to one another. They are so set into the body that 

 the basal joints, or, as they are called, the coxal joints, nearly 

 touch. This is the case in almost all Chilognatha, except in the 

 Polyxenidae, and it is a fact connected with some important 

 features in the internal anatomy. Then we have the peculiarity 

 in the Chilognatha which has formed the basis of most classifi- 

 cations which have placed these animals in a group by themselves. 

 This is the possession in most segments of two pairs of legs. 

 This characteristic has caused the group to be called by some 

 naturalists Diplopoda. As a general rule, the first four segments 



