Starting with your organic intersections at the beginning, these are really well done. You're doing a great job of capturing how the forms pile up on top of one another in a believable fashion that really sells the fact that they're all 3D. The only issue I noticed was that on the first page, with the top form on the left side of the pile, it appears to have a cast shadow that just stops halfway through. We have a shadow being cast by its tip, and one being cast by most of the back portion, but between there's a gap.

Moving through your animal constructions, I can see that you're wrapping your head around how to apply different concepts - for example, I'm seeing a well developing grasp of how to apply the sausage technique to construct legs that flow gesturally while maintaining a sense of solidity. Some of the contour curves you use to reinforce the joints do come out a little shallow though - remember back to the organic forms with contour curves exercise from Lesson 2, and how we encourage students to overshoot their curves to really show how they hook back around - don't be afraid to do that here.

I can also see numerous places where you're trying to use the additional masses, though there are some issues in how you employ them that I'd like to correct and clarify. The main issue is that when you add a mass to a structure, you appear to be thinking about it largely as though you're stamping a flat, two dimensional shape onto the page, then trying to figure out how to make it 3D (sometimes through the use of contour lines). The main thing we want to be doing is ensuring that as we draw it, we craft the silhouette of our additional mass in such a way that it actually conveys how it wraps around the underlying structure, and how it integrates with it. Take another look at the section on additional masses I linked at the beginning of this paragraph, and look closely at the little blue arrows that show how I've wrapped the silhouette around the existing structure of the animal.

We want the mass to feel as though it is tightly bound to the body - not that it merely sits atop it like a hat that can be knocked free easily, and definitely not like a flat sticker that has been pasted on top. Contour lines added after the fact can't contribute much to this end - they can, to an extent, make the form feel 3D by wrapping around the form in a way that describes how that surface moves through space, but what we're really doing here is using the mass itself as a contour line for the structure (in how it ends up wrapping along its surface).

The key to construction is ensuring that every element added in successive phases is a solid, 3D form - not just a shape or a collection of lines - and that its relationship with the existing structure is clearly defined in three dimensions. You are doing this to varying degrees and in certain places, but there are a lot of spots where you skip this important step.

For instance, looking at this deer's neck, there's no clear established relationship that defines how it connects to the torso. Here's a demonstration of how that would be approached (along with a bunch of other notes regarding the additional masses discussed above.

The key thing throughout all of this is that we need to focus on establishing simple forms and understanding how they exist in 3D space and how they relate to one another within that 3D space. The more complex you attempt to make your forms - for example, the deer's hooves - the harder it is to keep that straight in your head. That's why we build up to that complexity.

Another issue I noticed throughout your drawings was that you have a strong tendency to make your animals' cranial balls massive. Definitely try and start out with smaller ones. As far as eyesockets go, your follow-along with the otter drawing's face structure turned out well (all the different facial components fitting together like a 3D puzzle) but you appear to have stopped doing this for most of your own drawings.

Lastly, ease up on the fur and detail - I think it's serving as a bit of a distraction right now, so for the time being it's best to focus in on the underlying structure and nailing the illusion that all the forms you're fitting together are three dimensional before adding further detail.