Growing embryos

"The Raptor took shape inside its egg and I watched it on the ultrasound monitor. It looked like a ghost, or a puff of smoke."

- John Hammond

When the dinosaur nucleus, containing all chromosomes, is created the nucleus has to be injected into a unfertilised egg cell. Such cells are called s. This cell will multiply itself, forming an embryo. The embryo can only develop into a dinosaur if it is inserted into an egg.

Artificial eggs
In the book, Henry Wu claims that egg yolk is nothing but a growth medium that can be created in a laboratory. However, if it were this simple, an embryo could just be put into such a growth medium and left to grow (a scene in seems to show that some embryos were placed in tanks and that the scientists achieved some success because the embryos did grow big enough to be visible.

Extra hormones are needed from the original parent specimen, however, or constructed precisely from using the genome in order for the embryo to flourish.

Bird eggs
"Our fertilization department is where the dinosaur DNA takes the place of the DNA in unfertilized emu or ostrich eggs."

- Tour Voice

In the movie, and  eggs are used for this purpose. However, the development of an embryo is regulated by hormones in the egg/uterus and the environment. These (bird or crocodilian) hormones need to have the same effect as their original dinosaurian counterparts.

For that, they have to be able to recognize particular pieces of dinosaur DNA. In the novel, plastic eggs were used. However, such artificial environments do not exist yet, and are unnecessary. In The Science Of Jurassic Park And The Lost World Or, How To Build A Dinosaur, Rob DeSalle and David Lindley say that it would be a better idea would be to insert the fertilized ovum into a chicken/ostrich/chickenosaurus, and leave a natural egg to form around it.