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respiration is aerial, by means of tracheae or of pulmonary 

 chambers: The head and thorax are amalgamated. There 

 are no antennae and no abdominal legs, all the 8 legs 

 proceeding from the cephalothorax. 



1.183. Myriapoda\\a.ve a larger number of feet than even 

 the Crustacea. The head is quite distinct, the thorax and the 

 abdomen being amalgamated into one uniform chain of rings. 

 There is a pair of antennae Respiration is by means of 

 tracheae ending in distinct spiricles. 



1.184. Insecta. This order will be more fully described 

 in the next Chapter. 



1.185. Mollusca. These are soft-bodied animals, usually 

 provided with a covering shell. The body is without any dis- 

 tinct segmentation. The' nervous system consists either of a 

 single ganglion or scattered pairs of ganglia. Heart and 

 breathing organ are sometimes absent. The Mollusca are 

 classified under two divisions, via. } Mulluscoida and Mollusca 

 proper. The Molluscoida have their heart either entirely 

 absent or quite rudimentary. The nervous system consists 

 of one ganglion or a pair of ganglia. Brachiopoda, the 

 bodies of which are enclosed in a bivalve shell and Polyzoa 

 are examples of this Division. The Mollusca proper have 

 a well-developed heart with two chambers. This division 

 consists of univalve and bivalve animals. To the former 

 belong the Cephalopoda (e.g. ammonites) and Gastropoda 

 (e.g. whelks). To the latter belong Lamellibranche (e.g. 

 oysters and mussels). 



1. 1 86. Vertebrata. These are characterised by the pos- 

 session of an ento-skeleton definitely segmented. The nervous 

 centres are dorsal and shut off from the general body-cavity. 

 The limbs are away from the nervous centres and never 

 more than four. In most cases the adult has a vertebral 

 column. 



1.187. Pisces. Fishes are characterised by possessing a 

 gill ; their heart consists of only one auricle and one ven- 



