, 14 Inverlebrata. 



that in point of complexity the sub-kingdoms overlap 

 each other. 



The first sub-kingdom, Protozoa, includes those 

 animals which have neither body-cavity nor nervous 

 system, and are single celled. 



Sub-kingdom 2. Polystomata, includes sponges, 

 which have an internal cavity with a three layered wall, 

 one outlet, and usually many inlets, but no differ- 

 entiated organs, though consisting of many cells. 



Sub-kingdom 3. Coslenterata, includes jelly-fishes 

 and sea anemones, having a stomach cavity and a 

 body cavity as an outgrowth therefrom, and a radiate 

 symmetry. 



Sub-kingdom 4. Echinodermata, includes star- 

 fishes and sea-urchins, with a body cavity separate 

 from the stomach, a nervous system, and a system of 

 water-tubes which are agents in locomotion. 



Sub-kingdom 5. Vermes, includes worms which 

 are bilaterally symmetrical, and composed of successive 

 similar segments, with no jointed limbs, and with a 

 water- vascular system which has no locomotory func- 

 tion. 



Sub-kingdom 6. Mollusca, includes oysters, snails, 

 &c., possessing soft bodies enveloped in a leathery 

 mantle, no jointed limbs, a circulating system, often 

 an external shell and often an unsymmetrical nervous 

 system. 



Sub-kingdom 7. Arthropoda, includes crabs, 

 lobsters, spiders, and insects, which have bodies made 

 up of successive joints, with a symmetrical nervous 

 system, an external skeleton and jointed limbs. 



Sub-kingdom 8. Vertebrata, including fishes, 



