The first two are from observing "live" objects (is there a term I should use when describing objects from life?). Anyway...I used my own shell. It took many attempts at adjusting the shape, angles and line lengths when drawing the shell. It took fewer tries for the dolphin (I erased most of what I originally drew for the dolphin), thankfully. Enveloping an object is definitely more challenging than a ref. photo; I had to keep my eyeline in same place bc when I shifted my head or body, the shape and shadows on the object changed. The envelope was helpful because it reminded me that I need to keep the block in within the lines; when I was drawing the block-in for the dolphin, I had wanted to lengthen portions of it in at least 2 places so this helped me to maintain more accurate proportions. The envelope for elephant was done quickly (once with minor tweaking). Again, the envelope reminded me to restrict the size of its head (I wanted to make it so much bigger). How much detail should be included for the block in?

This is new to me. I found it challenging. I haven't tried this technique from a life drawing study yet. Gulp, I think I need to practice a bit more before I attempt that.

Something new to me, hard, but just keep practice.

Very good lesson ( orig. taught by the 19th Century French artist, Charles Bargue). Thank you for teaching this important concept.