BUDS INDUCED IN CLYMENELLA TORQUATA BY IMPLANTS OF NERVE CORD AND NEIGHBORING TISSUES DERIVED FROM THE MID-BODY REGION OF WORMS OF THE SAME SPECIES

¹ From the College of the City of New York and the Marine Biological Laboratory, Woods Hole

The data presented in the present paper and in the two related papers previously published (Sayles, 1940a and b) may be summarized as follows.

When oriented with their anterior ends out: (1) implants which include the eighth or more anterior segments will produce definitive head or tail buds with the type dependent to a considerable extent upon which segment of the host is involved; (2) implants including only segment 9 or segments 9-10 will also produce both general types of buds but probably not as frequently as implants from more anterior sources; (3) implants from segment 10 or segments 10-11 occasionally form a head or tail bud; (4) posterior implants which do not include any material from a level anterior to segment 11 very rarely, if ever, produce determinate buds.

When oriented with their posterior ends out: (1) anterior implants involving no cord posterior to the ninth segment produce no head or tail buds; (2) implants including only segment 10 or segments 9-10 rarely give rise to these buds; (3) implants including only segment 11 or segments 10-11 give rise to head and tail buds in many cases; (4) posterior implants including only segment 11 or more posterior segments produce tail buds frequently, but head buds rarely, if ever.

These data indicate that: (1) There is a tail-determining factor which is strong in the posterior half of the body but weak or absent at the level of segments 1-8. (2) There is a head-determining factor which is strongest in the anterior region of the body, weaker in the mid-body region, and perhaps finally absent in the posterior part of the worm. (3) The tail-determining factor at maximum strength is distinctly stronger than any head-determining factor in Clymenella.