To undergo embryonation.

Technically, this would apply to any situation in which a biological being was undergoing a rapid state of growth. Generally, a given creature has one stage in which it undergoes its most rapid growth, and this is labeled its embryonation. In practice, this stage of most rapid growth almost always takes place shortly after fertilization of the ovum. 'Embryonate' is most often used (in my experience, supported by Google) when talking about helminthes, as they have a habit of not-growing until the conditions are right. In the case of helminths, embryonation does not occur at a fixed age, and the environmental trigger that causes embryonation is of great interest to those trying to control outbreaks of various parasites.

Containing an embryo; having an embryo. Impregnated.

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