What are three substances that the embryo needs to grow and one substance it needs to excrete

Development of the fetus  to grow

oxygen for respiration. nutrients (food and water)

The developing fetus also needs its waste substances removing. The fetus is protected by the uterus and the amniotic fluid , a liquid contained in a bag called the amnion.

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is called echinoderms

after receiving a stimus, the sensory receptors send(s) signals to the appropriate area of the body.  

the must be sensory neurons.  

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