Abstract
1. Regeneration of the mandibular barbel The fry of the catfish possesses two pairs of mandibular barbels: one is permanent and the other is temporary. The temporary barbels degenerate and ultimataly disappear when the body length of the fry exceeds about 40 mm (ATODA, 1935). The regenerative ability of the temporary barbels may be expected to diminish gradually according to the increase in body length of the fry. The present paper reports on the regeneration of both the permanent and the temporary barbels of the fry measuring 20 mm and 35 mm in total length, respectively. In 60 animals, the distal one-third of a pair of right mandibular barbels was amputated.
In the 20 mm long fry, the permanent and the temporary mandibular barbels were similar in the processes of regeneration. Within six hours after amputation, a two-cell layer of epidermis covered the wound area, and perichondrial cells infiltrated into the space between the end of the cartilaginous rod and the overlying epidermis. By approximately twelve hours after amputation, the perichondrial cells mentioned above increased in number and oriented at a rigth angle to the axis of the cartilage. The accumlation of the perichondrial cells represents the initial formation of blastema of cartilaginous rod. By about three days after amputation, the blastema differentiated into cartilaginous rod, and incipient terminal buds appeared in the epidermis of the regenerate. Once the cartilaginous rod blastema had been formed, the regenerate elongated at the rate of about 0.25 mm per day at temperatures varing between 20-23°C, and attained the similar length and structure to those of the intact barbel by five days after amputation.
The processes of the regeneration of permanent barbels of the 35 mm long fry were similar to those of the barbels of the 20 mm long fry, except that the former needed more time than the latter in accomplishment of the regeneration.
The temporary barbels of the 35 mm long fry showed degenerative figures in their structure, and failed to regenerate normally. One day after amputation, the end of the barbel stump was barely covered with a layer of epidermal cells, but the accumulation of the perichondrial cells did not occur,
2. Histology of the mandibular barbel of three catfishes of Lake Biwa Three species of catfishes of Lake Biwa can be distinguished from their morphology and mode of life (TOMODA, 1961, '62). TOMODA (1961, '62) found that the mandibular barbel of Parasilurus biwaensis, a member of the catfises, was short and very feeble. He suspected that the barbel might be little effective as a sensory organ (personal communications). However, the present observation revealed that there were no great differences in histological structure among barbels of these three catfishes.
