We have the cardiac muscle, we have the smooth muscle and we have the skeletal muscle. Now, because we form the cardiac muscle, that means we also form the cardiovascular system of the body and that includes the heart as well as the blood vessels. We also form the excretory system as well as the reproductive system. So that includes the gonads of the female, the ovaries, as well as the gonads of the male, the testes. So these are the three different layers that are formed during the process of gastrelation. The question is, how does gastrolation actually take place?