The first sign of complexity comes on day I9.  A sheet of tissue forms down the middle. It isn't entirely flat: its edges furl in the middle and by way of a transverse sec­tion through the mass you would see that it forms a shallow U. The next day the U has become acute. Folds appear and disappear, slabs meld into one another.  Two more days and its vertices have met and touched in the middle. A moth folds its wings.  A squeamous tract forms, its walls replicate and condense into tiny nodules.  The nodules swell and invert whilst replicating continuously in a mitotic fashion.  Multiplication increases exponentially, a vascular sac gradually undergoes modification.  A feeding organ is introduced which causes the inhibition of a pathway.  Relaxation factors occur as a result of the severe cytokinesis. 

The whole thing zips up; a new growth forms a hollow tube that runs most of its length.  Small brick-like blocks of tissue appear either side, at first just a few, but then ten, twenty, and finally forty-four. They reach around to meet their opposite numbers and encase the tube. Underneath, the endoderm embraces an enormous, flaccid prosthetic mass.  Both retract up into layers of bones and a lightweight folding material is introduced. A distended gut shrivels.  Two halves of an ovipositor that had previously divided are drawn together. Inconspicuous tubes, one on either side, then unite to make a single larger tube running the length of the slab.