PHYSIOLOGY OF THE INVERTEBRATA. 



41 



Myriapoda have been divided into four orders ; and as two 

 of these contain only fossil genera they do not come under 

 our notice. 



In the Chilopoda (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 thd 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 Diplopoda or Chilognatha 

 (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 under-lip. The 

 digestive system (like the Chilopoda, 

 is a simple tube with salivary 

 glands. 



(4) The Thysanura represent the 

 first order of the Jnsecta, and are 

 said to resemble the young Blattce. 

 The mouth is provided with mandibles and maxillae. The 

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

 terminal portion. There are well-marked salivary glands, 

 and according to Sir John Lubbock Lepisma is provided with 

 four Malpighian tubules ; but certain genera of the Thysanura 

 (e.g., Japyx, Gantpodea) are devoid of these excretory organs. 



(5) The OrihopUra comprise the cockroaches, crickets, 

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

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



Fig. s. 



Alimentary Canal oi' 

 THE Chilopoda. 



m = mouth. s = salivary 

 glands, i = intestine. 



