Starting with your organic intersections, these are largely well done. You're establishing how these forms interact with one another, and conveying a strong illusion of gravity in how they slump and sag over each other. It gives a sense that each one has its own weight and thickness to it.

Looking at your animal constructions, there are areas in which you're demonstrating a good grasp of certain concepts of constructional drawing, and others where there are some issues in how you approach things. All in all, you're moving in the right direction, but there are some things I'll want to sort out and clarify for you.

To start, it's clear that you understand the importance of relying on the sausage method for constructing your animals' legs . There's only a couple places where you deviate from them somewhat, and in those cases it's usually more a matter of not quite adhering to all of the sausage-method principles as closely as you could. Just remember above all else that the sausage method is all about working with simple sausage forms - that means two equally sized spheres connected by a tube of consistent width. Don't let the ends be of different sizes, don't let them get wider through their midsection, etc. Also, as you've done correctly for the most part, the contour lines go right on the joint between sausage forms to establish how they intersect with one another. As I'll get into in a moment, there is no need to place additional contour lines through their midsection.

Now, you will find plenty of animals whose legs don't quite match the appearance of a chain of sausages on the surface. This is perfectly normal - you should still be applying the specific recipe of the sausage method (ends of same size and all that), because our primary focus is on creating an underlying structure or armature that captures both the illusion of solidity, and that of the gestural flow of the limb. Once those are in place, we can always go back and add additional masses to the structure as shown here to add bulk where necessary. In just about all cases, legs are going to have a lot more complexity to them, so don't be afraid to look more closely at your reference and identify the complexity you still have yet to build up. You can see an example of how legs can be pushed much further here.

The next thing I wanted to address was how you're going about tackling head constructions. While you are indeed thinking in terms of 3D forms and attaching them together - and that's fantastic - I am noticing a tendency to have, at least in some cases, components of the head floating more loosely instead of being firmly grounded against one another. As you can see in this demonstration, it's important to treat all the components of the head as parts of a "3D puzzle", which all fit together. Ideally you'll find the eyesocket buttressed by the brow ridge, the muzzle, the cheek bone, etc.

In earlier drawings especially, the components of the head felt less grounded, but in later drawings there was some improvement on this front.

The next issue I want to address is about working in 3D versus working in 2D. Being that we're employing constructional drawing - an exercise that is focused on developing a strong illusion that we're actually building something in a three dimensional space - it is critical that every change we make to our structure, every addition and subtraction, be done in 3D space. Since we're drawing on a piece of paper, we have a great deal of freedom to put down whatever kind of mark we wish, and as such, we have the freedom to make all kinds of mistakes that will undermine the illusion we're trying to create. That's what it comes down to - we have to restrict ourselves quite a bit to only working in steps that will further reinforce the illusion we're trying to create.

So, take a look at this image. There you'll see two lines marked out. The blue one defines a box form - something three dimensional - you constructed to attach to the head. The red line, however, doesn't appear to define a specific form - instead, it appears to take the silhouette of the cranial ball and the blue box form, and change how it sits on the page. This is a change that exists in 2D space - not 3D space - and it reminds the viewer that what they're looking at is in fact just a flat drawing.

Every change you make to your construction - as shown in the tapir head demo I linked further up - should consist of solid, three dimensional forms, and changes to those forms in 3D space.

Now, I've laid out a number of issues, so I'm going to tackle just one more before giving you some additional work to allow you to explore these principles on your own.

When adding your additional forms, you tend to draw the outline of the given form without too much thought to how it actually wraps around the existing structure, instead going back to add lots of contour lines in order to make it feel three dimensional on its own. This doesn't actually work that well, as shown here.

Contour lines that sit along the surface of a single form only serves to make that one form feel three dimensional on its own, in isolation. It doesn't tell us how that form sits on the surface of the object, and therefore how it integrates with the construction as a whole, and this is what actually matters most of all.

These kinds of contour lines actually are pretty limited in how useful they can be, primarily because they suffer from diminishing returns. That is to say, adding the first one may help make a form feel really three dimensional, but the second will only help reinforce the first. Adding a third, and a fourth, will contribute less and less, to the point that they're probably not going to serve any useful purpose. When students have a tendency to just cover their constructions in contour lines (as you've done here), it's more because they're working based on what they feel they're supposed to be doing, but not actually thinking about why they're putting down those marks. It's critical that when you put a mark down, when you're applying the planning phase of the ghosting method, that you ask yourself what the "job" you want a mark to accomplish is supposed to be, whether it is the best mark for that task, and whether another one may already be accomplishing it for you.

There are however other kinds of contour lines which can be much more effective - for example, the contour lines that define the relationship between two forms, or the "intersection" between them - like the contour curve that sits at the joint between two sausage segments. These, when drawn properly, will create a strong connection in 3D space, often making any further contour line entirely unnecessary.

The principle of contour lines can also be achieved through entities other than lines altogether - for example, the way we wrap our additional masses (as shown here) around the existing structure works the same way that we'd wrap a contour line around it. In doing this, we're creating another kind of bond between two 3D forms, establishing how they relate to one another in 3D space, and immediately convincing the viewer that both are in fact three dimensional and not just flat shapes on the page.

To this point, it's important that you remember how these additional forms need to wrap around any part of the structure they come in contact with - this means that if you add an additional mass along one section (like the big hip muscle), and then add another additional mass long the rump, it will inevitably wrap around the hip muscle mass, since that is now part of the existing structure. Similarly if you added any additional masses along the back, instead of just overlapping the one on the rump, you'd have to wrap around it in a convincing manner. It's like piling meat onto the structure of the animal - if something's already there, you can't just ignore it, it has to be respected.

So! I've covered a lot of areas that you can work on, so as I mentioned before, I'll leave you to tackle that on your own with a few additional animal drawings. I highly recommend that you take a look at some of the newer demonstrations on the informal demos page - those towards the top of the page are the newer ones before tackling the additional assigned pages.