The network or mass of blood capillaries enclosed within the Bowman's capsule is called the glomerulus. This is where the first step of urine formation, known as ultrafiltration, takes place, as the blood pressure forces water and small solutes out of the capillaries and into the capsule's space.

A. tubule: The renal tubule is the long, convoluted structure that extends from the Bowman's capsule (specifically, the proximal convoluted tubule). The filtrate flows into the tubule after being collected in the capsule, and further reabsorption and secretion occur here, but it is not the capillary mass itself.

B. pelvis: The renal pelvis is a funneled region in the kidney that collects urine from the collecting ducts and channels it into the ureter; it is not located within the Bowman's capsule.

D. nephrone: The nephron is the entire functional unit of the kidney, which includes both the renal corpuscle (glomerulus and Bowman's capsule) and the renal tubule, along with its associated capillaries. It is an entire structure, not a component part of the Bowman's capsule.