The rest of it can only be seen

Rosalie Blanche & Jermaine Lulham, An introduction to Zoology, with Direction for Practical Work (Invertebrates), Londres, MacMillan, 1913, p. 317-321.

The larvae hatch out after to three weeks and at once begin to make for themselves little protective case out of any suitable material that may be at hand in the water. When the larva is full grown, its case has usually a characteristic appearance according to the species which has made it. One such case is shown in Fig. 242 P with the caddis-worm projecting from one end. The larva under normal condition never more exposes more than its head and the first three segments of the body, all of which are protected by a brown chitinous skin. The rest of it can only be seen when it has been induced to leave one case. This is easily accomplished by cutting the case carefully open, or by prodding it from behind very gently with the head of a pin or some other blunt object ; the caddis-worm will then, though apparently with great reluctance, leave its case, and expose the soft defenceless hind, end of its body.