PHYSIOLOGY OF THE INVERTEBRATA. 



41 



Myriayoda have been divided into four orders ; and as two 

 of these contain only fossil genera they do not come under 

 our notice. 



Ill the ChUopoda (centipedes) the body is usually long- and 

 segmented ; each segment carrying a pair of many-jointed 

 limbs. The first and second pairs of limbs are masticatory, 

 while the fourth pair are known as poison-claws. The head 

 is flattened and the mouth is constructed for biting. The 

 mouth leads into a long oesophagus, followed by an alimentary 

 canal which is usually straight, some- 

 what like the intestinal tube of cater- 

 pillars. There is a pair of salivary 

 glands (Fig. 5) which pour their 

 contents into the mouth. 



(3) The Diployoda or Chilognatlia 

 (millipedes) have rounded bodies, 

 which are segmented. There are two 

 pairs of limbs on each segment ex- 

 cept the anterior one. The first pair 

 of maxillae is represented by a four- 

 lobed buccal plate or undei'-lip. The 

 digestive system (like the Chilopodc, 

 is a simple tube with salivary 

 glands. 



(4) The Thysanvra represent the 

 first order of the Inseda, and are 

 said to resemble the young Blatta:. 



The mouth is provided with mandibles and maxilla3. The 

 alimentarv canal is divided into a buccal, a median, and a 

 terminal portion. There are well-marked salivary glands, 

 and according to Sir John Lubbock Ztpisma is provided with 

 four ^lalpighian tubules; but certain genera of the Tltysainira 

 {''.y., J'lpyx^ Campodca) are devoid of these excretoiy organs. 



(5) The Orthoptcra comprise the cockroaches, crickets, 

 dragon-flies, may-flies, grasshoppers, &c. The body is 

 divided (like all the Insaia) into head, thorax, and abdomen. 



Alimkntakv Canai, Ol' 



THK CHILOPODA. 



!!! = mouth. ^ = salivary 

 glands. / — intestine. 



