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Morphogenesis and form  ·  Article

Nerve cord dependence of head formation in regenerating earthworms

Loeb reported that Morgan found a new earthworm head can form only at the anterior cut end of the nerve cord.4 When a piece of the cord was cut away from the front, a head formed at the cord's cut end instead in some such cases.5 The result ties head formation to the nervous system and bears on how regeneration is controlled.

Earliest held
1896, Wilson, E. B.
Most discussed in
Regeneration, 1901
In the library
47 passages in 10 works
Rewritten
2026-11-06
18501875190019251950197520002025Wilson, E. B., 18961Morgan, T. H., 19012Morgan, T. H., 19013Loeb, J., 19064Loeb, J., 19065Loeb, J., 19066Loeb, J., 19127Loeb, J., 19168Tyler SEB, 20179
01

Early worm regeneration

Regeneration in worms was known long before these experiments. Morgan's 1901 review says Réaumur found that certain fresh-water worms and the terrestrial earthworm regenerated when cut into pieces.2 Morgan's own bibliography lists a 1899 paper confirming Spallanzani's discovery of an earthworm regenerating a tail in place of a head.3 Loeb's 1891 work on heteromorphosis, in which an organ is replaced by one of a different kind, is cited in Wilson's 1896 bibliography.1

02

Morgan's cord excision

Loeb described the experiment in 1906 and credited it to Morgan. A few anterior segments were cut off. A piece was then removed from the front of the nerve cord, leaving other tissues unchanged.5 The cut end of the body healed and formed no head. In some cases a head formed instead at the anterior cut end of the nervous system.5 If only the head was removed, a new head formed at the front of the body.6

03

Two cut ends, two heads

Loeb also described a second series by Morgan. The head was cut off and a further piece was excised from the nerve cord. This left two anterior cut ends of the cord.4 Loeb reports that in a few of these cases two new heads were formed.4

04

Nerve influence and later views

Loeb discussed other cases of nerve influence separately. In 1916 he cited Herbst's crustacean work, where removing the optic ganglion with the eye led to an antenna in place of an eye, while leaving it led to an eye.8 Loeb in 1912 also noted that some animals show heteromorphosis while others show strict polarization.7 Tyler's 2017 review mentions earthworms in a different context. It says each segment has a specific electric potential, and segments are added until the total field matches a full-sized worm.9

SourcesEach quotation was checked word for word against the passage it opens.
  1. Loeb, J. — Untersuchungen zur physiologischen Morphologie : I. Heteromorphosis. Wurzburg, 1891.Wilson, E. B., 1896 · The Cell in Development and Inheritance · open at passage 1020
  2. He found also that certain fresh-water worms, as well as the terrestrial earthworm, regenerated when cut into pieces.Morgan, T. H., 1901 · Regeneration · open at passage 10
  3. A Confirmation of Spallanzani's Discovery of an Earthworm regenerating a Tail in place of a Head. Anat. Anz., XV, 1899.Morgan, T. H., 1901 · Regeneration · open at passage 780
  4. Morgan has made a somewhat similar observation on earthworms, in which he found that a new head is only possible at the anterior cut end of the nerve cord.Loeb, J., 1906 · The Dynamics of Living Matter · open at passage 562
  5. The anterior cut end a of the worm healed, and no new head formed at this place. Instead, a new head was formed in some such cases at b, at the anterior cut end of the nervous system.Loeb, J., 1906 · The Dynamics of Living Matter · open at passage 562
  6. If the head alone is cut off in an earthworm without the excision of the anterior piece of the nerve cord, a new head is formed at the anterior end of the body.Loeb, J., 1906 · The Dynamics of Living Matter · open at passage 562
  7. while in some animals we are able to produce heteromorphosis, in others the most definite polarization existsLoeb, J., 1912 · The Mechanistic Conception of Life · open at passage 159
  8. The latter will take place when the optic ganglion is removed with the eye, the former when it is not removed.Loeb, J., 1916 · The Organism as a Whole, from a Physicochemical Viewpoint · open at passage 307
  9. in earthworm regeneration, each segment has a specific electric potential. Segments are added by regeneration until the total endogenous field potential is that of a normal full-sized wormTyler SEB, 2017 · Nature's Electric Potential: A Systematic Review of the Role of Bioelectricity… · open at passage 40
Linked ideas
Regenerationpart of / contains
The cord experiment is one case of regeneration, where the site of the new head depends on tissue left at the wound.
Polarityrelated to
Loeb contrasted animals with strict polarization to those showing heteromorphosis, a contrast the worm result bears on.
Head formation tied to the nerve cord connects to ideas about the head's special role in the body.
Child's index lists axial heteromorphosis and polarity among gradient topics, a framework in which head formation was discussed.
Tyler's review links earthworm segment potentials to regeneration, a bioelectric reading alongside the nerve-based one.
Another article on earthworms as organisms, here concerning the nervous system's role in body form.
Both concern head regeneration in worms. Child's passages show Planaria brain ganglia can form independently of cut nerve cord ends, whereas B says earthworm heads form only at the cord's cut end; A's memory claim isn't discussed.
Where it is discussedPassages matching new head at the anterior cut end of the nerve cord, excision of the nerve cord, earthworm regeneration, heteromorphosis
1901Regeneration · Morgan, T. H.13
1912The Mechanistic Conception of Life · Loeb, J.13
1906The Dynamics of Living Matter · Loeb, J.8
1916The Organism as a Whole, from a Physicochemical Viewpoint · Loeb, J.4
1921The Origin and Development of the Nervous System · Child, C. M.3
1900Comparative Physiology of the Brain and Comparative Psychology · Loeb, J.2
1896The Cell in Development and Inheritance · Wilson, E. B.1
2017Nature's Electric Potential: A Systematic Review of the Role of Bioelectricity… · Tyler SEB1
1906Behavior of the Lower Organisms · Jennings, H. S.1
1924Physiological Foundations of Behavior · Child, C. M.1