Answer: Hard Tick
This was definitely a challenging one - including for me when I first saw this case. I think that most of us are not used to seeing ticks cut in histologic section (usually this isn't necessary for identification!), but there are some characteristic features that allow for easy identification of this case.
First, notice that the organism is mostly external to the skin, and is inserted only at one end. This is the classic presentation for a tick, and would argue against a botfly larva which is mostly inserted into the skin.
In addition, there are useful identifying histologic features as outlined in the image below, including a thick sclerotized cuticle, well-developed skeletal muscle near the mouth parts, and the mouthparts themselves, if present. (CLICK ON IMAGE TO ENLARGE)