 Then, by crawling movements, the organism pushes forward in the old integumentary shell, which splits down the back allowing the animal to emerge.Often, this initial crack is caused by a combination of movement and increase in blood pressure within the body, forcing an expansion across its exoskeleton, leading to an eventual crack that allows for certain organisms such as spiders to extricate themselves.While the old cuticle is being digested, the new layer is secreted.