Secondaries – a group of multicellular animals. These include the most progressive animals – vertebrates (a subtype of chordates).
In the secondary ones, during the period of embryonic development, an anal opening forms at the site of the primary mouth, and the mouth itself appears independently in the front of the body. There is a secondary body cavity (whole).
Remember: The process of learning a person lasts a lifetime. The value of the same knowledge for different people may be different, it is determined by their individual characteristics and needs. Therefore, knowledge is always needed at any age and position.