Arriving in update 2.1.0, the Cultivator is a specialized type of Incubator that is used for gestating creatures that don't lay eggs.

The Cultivator comes in 16 different colour variations, corresponding to the different types of stained glass in the game. In order to craft this machine, you will need 4 stained glass panes (they must all be the same colour), 3 iron ingots, and a redstone comparator.

Cultivator crafting recipe

Cultivator (white variant) crafting recipe

The Cultivator has an input slot for water buckets, an input slot for DNA syringes, and an input slot for food. In order to cultivate an embryo, you will first need to insert three water buckets, and sufficient nutrients (in the form of food). Different types of food give different nutrient values: For example, meat, eggs and fish are rich in lipids, while plant products such as carrots and wheat contain more minerals and vitamins.
Cultivator GUI

Cultivator GUI, full of water

Next, set the temperature slider to decide the gender of the embryo (it works exactly like the Incubator). Finally, insert the DNA syringe (obtained from the Embryonics Machine) of a compatible species - such as that of a Coelacanth - and then wait for a few short minutes.

Gestated Coelacanth

Gestated Coelacanth item

Once the embryo has been grown, you will get a "gestated" creature. It resembles a juvenile of the species inside a little glass vat. Just like the Hatched Egg item, right-click on the ground with this item to spawn the baby animal!

If it's a marine/aquatic animal species (e.g. Coelacanth), then you will instead right-click in the water to obtain the same result!