To add to the excellent response above, I'd comment that Rotpeter's speech also reflects the theme of freedom—or rather, the difference between "freedom" and a "way out."

Rotpeter acknowledges that he may at some point have experienced "the spacious feeling of freedom on all sides" and in all directions back when he thought and acted like an ape. He trades that freedom—which would have meant death in an attempt to return to his home on the Gold Coast—for "a way out" of his predicament. His "way out" is humanity; he learns to mimic the behavior of the humans around him, which he (perhaps unintentionally) suggests is hardly superior to what his own natural instincts were. When he learns to spit like his handlers, he cleans his face while they do not ("I learned to spit in the very first days. We used to spit in each other's faces; the only difference was that I licked my face clean afterwards and they did not."). Perhaps the most unnatural habit he must acquire is a taste for alcohol. He says the smell "revolted" him—"I forced myself to it as best I could; but it took weeks for me to master my repulsion."

He works so diligently (and at such great cost) to alter his nature not because he wants to, but because this is his "way out";

"I repeat: there was no attraction for me in imitating human beings; I imitated them because I needed a way out, and for no other reason."

As a result, he says,

"I managed to reach the cultural level of an average European. In itself that might be nothing to speak of, but it is something insofar as it has helped me out of my cage and opened a special way out for me, the way of humanity. ...There was nothing else for me to do, provided always that freedom was not to be my choice."

Do we, Kafka's readers, sacrifice true freedom in all directions for the "way out" that gets us by? What do we give up when we civilize ourselves? Some think these were questions that Kafka himself was struggling with. He was committed to artistic freedom in his writing, but also felt the pull of responsibilities to family, society, work, and friends. Rotpeter, seeing the struggle that a quest for true freedom would result in, rejects it and chooses simply a path forward, an escape in social acceptability. Has Rotpeter benefitted? Is he happy? Is he extraordinary? Has his massive effort "to reach the cultural level of an average European" been worth it? Rotpeter says,

"In itself that might be nothing to speak of, but it is something insofar as it has helped me out of my cage and opened a special way out for me, the way of humanity. ... With my hands in my trouser pockets, my bottle of wine on the table, I half lie and half sit in my rocking chair and gaze out of the window: if a visitor arrives, I receive him with propriety. My manager sits in the anteroom; when I ring, he comes and listens to what I have to say. Nearly every evening I give a performance, and I have a success that could hardly be increased. When I come home late at night from banquets, from scientific receptions, from social gatherings, there sits waiting for me a half-trained little chimpanzee and I take comfort from her as apes do. By day I cannot bear to see her; for she has the insane look of the bewildered half-broken animal in her eye; no one else sees it, but I do, and I cannot bear it. On the whole, at any rate, I have achieved what I set out to achieve."

Has the life he describes really been worth the massive effort he expended to achieve it? What has not seeking "freedom on all sides" really earned him? His victory seems a hollow one.

One of the more interesting themes in this story is the civilizing process that the ape undergoes. Taken out of his natural environment and forced into captivity, the ape has no choice but to adapt to the ways of mankind and assimilate into society. He acquires language and learns the customs of those around him, including smoking, spitting, and drinking alcohol. His hope is that by becoming civilized, he will be able to leave the confines of his cage.

A close reading of the story reveals that society is not presented in a favorable light. The ape must exercise a great deal of control in order to follow the rules of civilization, and this restraint is evident in the academic and meticulous language that he uses to tell his story: "let me be particular in the choice of a word for this particular purpose, to avoid misunderstanding." His sexual urges are somewhat repressed, and he occasionally satisfies them with a half-trained ape that he later finds repulsive: 

When I come home late at night from banquets, from scientific receptions, from social gatherings, there sits waiting for me a half-trained little chimpanzee and I take comfort from her as apes do. By day I cannot bear to see her; for she has the insane look of the bewildered half-broken animal in her eye; no one else sees it, but I do, and I cannot bear it. 

The degree is freedom that his civilizing process has afforded him is rather ambivalent. He sums up his thoughts on his transition: "As I look back over my development and survey what I have achieved so far, I do not complain, but I am not complacent either." 

To put this story into some historical perspective, it would be interesting to compare A Report to an Academy (1917) with Freud's theories regarding repression, the power of the superego to dominate the id, and the repressive effects of civilization on the psyche. Like Freud, Kafka suggests that civilization does not ultimately lead to freedom or happiness and instead imposes its own confinement.