Hi, I'm currently going through this lesson but I'll try to give you some helpful advice.

Starting with your organic intersections, they are pretty well constructed and do convey a sense of 3D.

You mention that you had problems with head construction, if you're uncertain err on the side of drawing it smaller, this way you can always add up instead of trying to work in a substractive way. Drawing the cranial mass bigger than it should be, leads to some elements in the face feeling smudged.

Regarding the head planes, you could try to stick strictly to the demo shown here.

The eye socket is better off as a pentagon with the point facing downwards. This provides a wedge for the muzzle to fit into, and a flat edge across the top for the forehead/brow ridge to rest upon.

Here's a demoon how to draw eyelids that you may find helpful.

Now I have done comments on the way you draw additional masses, I am seeing that some of them are small and as such they don't really add a lot of useful information to the drawing, instead look for opportunities where you can wrap your masses around other structures especially the big masses you'll find in quadrupedal animals' shoulders and hips are especially good for this, though they might not always be obvious or easy to spot in your reference. They're always there as these animals have very large muscles.

The more things can fit together, the more cohesive everything will feel, yielding to a more solid overall construction.

And finally I have some advice to give you on the way you present your homework, but I don't really know if it applies here. Remember to give your drawings as much space and time as you can, I don't know what paper size you're using but if it is the standard size, you may want to fit in less drawings, take this advice only if this is the case.

So that's all I have to say.