Vayikra 11 (Shemini) - The structure of chapter 11

The structure of the chapter 11 demonstrates in a literary manner the idea of separation which is the idea of kedusha and is the theme of the chapter. The chapter can be divided based on whether the animals being discussed are referred to as a sherets (swarming) or not. 

11:2 is an introductory sentence, and the first laws are from 11:3-11:8, and these discuss behamot which are not sherets. 

11:9-12 record laws about fishes and the fish that are not allowed are referred to as sherets (11:10). 

The third set of laws, 11:13-20, are about birds, and these are not referred to as sherets.

The fourth set of laws are with regard to flying insects, 11:20-23, and these are sherets, 11:20,21,23. Note that 11:20 and 11:23 form a bookend around 11:21,22, which record which insects can be eaten.

The fifth set of laws, 11:24-28, is about the behamot and the hayyot, and again they are not sherets.

The sixth set of laws, 11:29-38, is about the land animals that swarm and they are sherets, 11:29.

The seventh set of laws 11:39,40 is again about behamot, and these are not sherets. 

The last set of laws 11:41,42 refers to eating animals that swarm, and these are referred to as sherets four times within the two sentences. 

The pattern of the chapter is non-sherets to sherets and back again, and this is written to show in a literary way the idea of separation, kedusha.