 Dear student, in this study you will learn about brains in different animals in relation to complexity of functions. Complexity of brain functions in different animals varies greatly and based on different factors such as evolutionary history, ecological niche and social behavior. Brains have evolved to serve specific functions that are advantages for animals, reproduction and survival. Dear student, in this study we will move from simple nervous system to complex nervous system. So first of all we will discuss simple nervous system or the nervous system in invertebrates. So invertebrate nervous system such as insects and Moleskine nervous system is the simplest nervous system. It consists of clusters of cells known as ganglia which are connected by nerve cords. Their brain are smaller in size and adopted to perform different behavior. It like the complexity of vertebrate brain. For example in insects there are special brain regions which are responsible for processing of visual and olfactory information and these information are crucial for navigation and finding of food. Now look at this figure A or the first image is about Hydra which is showing simplest nervous system that is NavNet. The second is about flatworm or here is planaria as you can see that. The nervous system of flatworm consists of simple linear nerves that are connected to a complex neuronal network. The next is analita and here is earthworm. In analita the nervous system consists of bilateral brain, a ventral nerve cord and segmental ganglia. The next is arthropoda and here is a crossover with segmental ganglia and more elaborated sensory organs. Next is fish and amphibians. The brains of fish and amphibians are more developed as compared to brains of invertebrate. They possess regions like forebrain, midbrain and the handbrain and these regions are involved in sensory processing, motor control and some basic cognitive functions. For example in fish there are well developed sensory areas which are involved in detection of light, chemicals and movement in water. Next are reptiles. The reptile brains are more developed and more complex brains as compared to brains of fish and amphibians. They exhibit improved sensory processing, special memory and problem solving skills. In some reptiles like in some species of lizards they show some advanced cognitive skills like learning and memory retention. Next are birds. Birds are known for their relatively large brain and complex cognitive skills. Pigeon bird region of forebrain is responsible for complex behavior like problem solving, tool use, communication and special memory. Some birds like pigeons, crows and parrots have demonstrated excellent problem solving skills in different laboratory experiments. Next group is about mammal. Mammals possess brains which are more complex and more advanced due to their evolutionary history and demand to nurture their young ones. Mammals brains are characterized by a highly developed neocortex which are responsible for some cognitive skills like decision making, language processing and complex social interaction. Some primaries including humans have large and intricate neocartices that are thought to be linked with their social behaviors and cognitive abilities. Dear student, I hope now you have complete understanding of brain and the complexity of brain functions in different animals. Best of luck. Thank you.