In the course of development, the invagination of stomodeum occurs earlier than that of proctodeum at the third and the sixth nauplius stages respectively.

• 在发育过程中,口凹是在第三期无节幼虫时内陷形成,而原肛是在第六期无节幼虫时内陷形成的,所以口凹的发生早于原肛的发生。