Calcitonin-immunoreactive cells of the digestive tract of the amphioxus are distributed concentrically in a restricted region of the mid-gut

In amphioxus (Branchiostoma belcheri), calcitonin-immunoreactive cells of t he digestive tract were distributed concentrically in a 1-mm region of the latter half of the mid-gut. In the mid-gut caecum these cells were also pre sent, but were dispersed throughout the length. The total number of cells i n both parts ranged from 280 to 1157, varying from individual to individual , although the number in the mid-gut caecum was only 100-200. These cells w ere morphologically typical gut endocrine cells. Considering their morpholo gy and the characteristics of their distribution pattern, these cells may b e related to some phenomena of digestive processes.