physiological approach to the lower animals

acid activity animal behaviour animal's annelids arteries arthropods bacteria bees blastocoel body cavity brain carbon dioxide central nervous cephalopod chemical circular muscles circulatory system coelenterates coelom concentration connexions contractile contraction coordination crustacea cuticle diffusion digestion dorsal earthworm echinoderms energy enzyme excretion excretory organs external medium fluid frequency fresh-water function ganglia giant fibres gland haemocoel heart insects intestinal invertebrates large number leech legs longitudinal muscles lower animals mammalian mammals means mechanism membrane molluscs motor nerve movements muscle fibres muscular Nereis nerve fibres nerve impulses nerve net nervous system neurones nitrogen ommatidium osmotic pressure oxidation oxygen oxygen tension parapodium physiological posterior reflex arcs region respiratory organ salts sea anemone sea water segment sense cells sense organs sensory nerve simple stimulation substances surface terrestrial animals through-conducting system tion tissues tracheal system tube tubule unstriated urine ventricle vertebrates vessel waggle waggle dance wall worm