It is not necessary to tell the reader what is being hatched and by not doing so it is adding to the tone of the scene. We see the Director rattling off statistical information and the students dutifully writing everything down. This gives the reader a picture of a very orderly and controlled world. In fact, the entire scene is reminiscent of an assembly line.  This image will be repeated in the novel several times to evoke the idea of Henry Ford on whom the society has in part modeled themselves.  

The reader is to understand that in this world, individuality is not important and that all human beings are created under the same circumstances. Later on, as the novel develops we learn of how there are different classes but there is no class envy since that is socialized out of them by behavioural conditioning. So the initial scene we have in the hatchery sets the physical and emotional tone of the novel.