REGENERATION IN ANNELIDS
197
A. Experimental Facts
1. Cephalic Regeneration
In oligochaetes, Kropp, as early as 1933, tried to demonstrate a
hormonal influence of the nervous system by injecting nerve cord extracts and by grafting the brain. After decerebration and ablation of the
nerve cord, nerve cord extract was injected near the amputation surface,
but this had no effect on cephalic regeneration. He also implanted a
brain dorsally or ventrally in the segment next to the wound surface.
When the grafts were implanted dorsally, they were soon isolated by
connective tissue ; however, if they succeeded in fixing themselves to the
body wall, they could subsist for a month or so in a sound and well
vascularized state, but later on they were absorbed by phagocytes.
These grafts, which had no relation to the rest of the nervous system,
seem to have had the sole effect of retarding cephalic regeneration.
When the grafts were placed ventrally ahead of the cut end of the nerve
cord, they remained sound and established a connexion with the regenerating fibres from the cord and thus were embodied in the nervous
system of the regeneration bud.
In 1943, Okada and Kawakami used brain implants to bring about the
appearance of supernumerary heads. They established that a brain
grafted under the epidermis can survive only if it adheres closely to the
body wall ; in this position, if the period of survival is long, a small nonsegmented regeneration bud develops, but the bud is less well developed
than when the nerve cord is diverted to the epidermis. Extracts of the
nervous system, when injected in the same region, have no effect. In
these experiments, the difficulty lies in keeping a living brain in the
tissues of an oligochaete. In these animals, as soon as a foreign body
comes in contact with coelomic components, it is immediately surrounded by amoebocytes and then destroyed by phagocytosis.
It seems that, in polychaetes, brain grafts are more easily maintained.
In 1948, Harms experimented on Lycastris, a species which does not
normally show cephalic regeneration at any level. After decapitation,
he grafted several brains in the healing zone and initiated cephalic re·
generation. It seems, therefore, that the brain could have some endocrine function in cephalic regeneration. However, the data available at
present are not sufficient to ascertain what part it plays and further
experiments with detailed histological observations are necessary for a
more thorough understanding.
2. Caudal Regeneration
Hormonal effects of the brain on posterior regeneration are more
easily demonstrated by experimental ablation and simultaneous graft-
197
A. Experimental Facts
1. Cephalic Regeneration
In oligochaetes, Kropp, as early as 1933, tried to demonstrate a
hormonal influence of the nervous system by injecting nerve cord extracts and by grafting the brain. After decerebration and ablation of the
nerve cord, nerve cord extract was injected near the amputation surface,
but this had no effect on cephalic regeneration. He also implanted a
brain dorsally or ventrally in the segment next to the wound surface.
When the grafts were implanted dorsally, they were soon isolated by
connective tissue ; however, if they succeeded in fixing themselves to the
body wall, they could subsist for a month or so in a sound and well
vascularized state, but later on they were absorbed by phagocytes.
These grafts, which had no relation to the rest of the nervous system,
seem to have had the sole effect of retarding cephalic regeneration.
When the grafts were placed ventrally ahead of the cut end of the nerve
cord, they remained sound and established a connexion with the regenerating fibres from the cord and thus were embodied in the nervous
system of the regeneration bud.
In 1943, Okada and Kawakami used brain implants to bring about the
appearance of supernumerary heads. They established that a brain
grafted under the epidermis can survive only if it adheres closely to the
body wall ; in this position, if the period of survival is long, a small nonsegmented regeneration bud develops, but the bud is less well developed
than when the nerve cord is diverted to the epidermis. Extracts of the
nervous system, when injected in the same region, have no effect. In
these experiments, the difficulty lies in keeping a living brain in the
tissues of an oligochaete. In these animals, as soon as a foreign body
comes in contact with coelomic components, it is immediately surrounded by amoebocytes and then destroyed by phagocytosis.
It seems that, in polychaetes, brain grafts are more easily maintained.
In 1948, Harms experimented on Lycastris, a species which does not
normally show cephalic regeneration at any level. After decapitation,
he grafted several brains in the healing zone and initiated cephalic re·
generation. It seems, therefore, that the brain could have some endocrine function in cephalic regeneration. However, the data available at
present are not sufficient to ascertain what part it plays and further
experiments with detailed histological observations are necessary for a
more thorough understanding.
2. Caudal Regeneration
Hormonal effects of the brain on posterior regeneration are more
easily demonstrated by experimental ablation and simultaneous graft-