As a whole I think you're doing a pretty good job. You're showing a lot of signs that you've paid a good deal of attention to how your constructions consist of simple forms that exist and relate to one another in three dimensions, and the way in which you're laying those forms out and building them upon one another shows good observational skills and strong study of your reference images.

There are just a few issues I want to address - some of them show improvement over the set, but others are more notable and require a bit more attention.

The first issue that stood out to me was that early on, you were drawing your eyesockets as simple ellipses. As you moved through, you did improve upon this, breaking them down into individual straight lines being cut into the surface of your forms. That said, there is still room for improvement. What I want you to think about when drawing your eye sockets is that these often mark the first step of taking rounded surfaces and breaking them into a series of planes. The edge of the eye socket define one edge of many different planes of the face - moving forward we can extend these out into the muzzle, for example, which itself will be separated into planes, but the eye socket is where it starts.

The second issue has to do with how you're drawing a lot of your additional masses - especially those that sit on the joints of the legs, but also in some cases with the bigger ones sitting on the torso itself. You have a tendency of drawing them as arbitrary blobs without actually considering how that form is going to wrap around the underlying structure. As shown here, when drawing the outline of your next additional mass, how you draw it is either going to make it look like a three dimensional form wrapping around the existing structure, or it's going to make it look like a flat shape that has been pasted on top. You can also see examples of this in these notes.

Related to these additional masses, one thing I want you to stop doing altogether is wrapping your structure (additional masses and all) in a final outline. You can see what I mean by looking at this donkey, specifically this leg where I've marked out little areas in red. Basically it looks like you drew a final outline around the entirety of the leg, and bridged across small areas, altering the silhouette that resulted from the 3D forms themselves. Don't do this - if you want to add some structure that fills in a gap or bridges across a space, do so with another 3D form. The silhouette should be the result of the 3D forms you've combined, not an artificially created shape you've drawn in one go on the page.

Aside from these points, your work in this lesson is coming along quite well. I'll go ahead and mark this lesson as complete, so just be sure to practice the points I raised on your own.