318
TH. LENDER
studied very extensively and has been well understood since the
investigations of Vandel (1922) on Polycelis cornuta and Planaria
alpina. His paper is a good source of reference to the earlier work.
It is clear that the entire sexual apparatus arises from the differentiation
of the neoblasts. With regard to the genital glands, Dubois (1949)
showed that, after X-irradiation, an ovary is reconstituted from the
neoblasts during regeneration (Fig. 7). The differentiation of the
copulatory apparatus from the neoblasts occurs on the spot without
anatomical relations with the genital glands (Vandel, 1922; Kenk, 1924;
Nobili, 1958). The ducts for conveying the genital products form last.
In Polycelis tenuis, Lender and Le Moigne (1960) distinguish three
phases in the regeneration of the copulatory apparatus (Fig. 8). At the
start, a concentration of neoblasts is visible in the genital region; in the
mass of cells two cavities form which turn into the genital atriums.
During the second stage, a bud differentiates into a penis in the male
atrium and the deferent ducts, as well as the copulatory pouch, are
formed. In the third stage, formation of the penis is completed, the
oviducts become hollow, the deferent ducts continue to progress towards
the testes, and the musculo-glandular organs appear.
Naturally the factors which release this morphogenesis have been
investigated. Vandel (1922) was the first to analyse the determinism of
the regeneration of the genital organs of Polycelis cornuta. He found that
the appearance of the copulatory apparatus was not induced by the
brain or the ovaries. Unfortunately, it is difficult to castrate a planarian
since the testes are situated on each side of the body from the cephalic
region to the level of the genital organs. Vandel caused degeneration of
the testes by raising the temperature of the water in which the planarians
Polycelis cornuta and Planaria vitta were raised, or by introducing a
parasite. Under these conditions the copulatory apparatus did not
regenerate. Vandel, while emphasizing the imperfection of his methods,
postulated that the testes emit substances which cause the differentiation of the genital organs.
But there is another way to attack the problem. One and the same
species may exist in nature in two forms, an asexual form and a sexual
form. Vandel (1925) considered Planaria (Dugesia) subtentaculata of
Southern France to be the asexual form of Dugesia gonocephala. In
America, there is an asexual and a sexual form of Dugesia tigrina
(Planaria maculata) (Kenk, 1937; Hyman, 1939, 1943). In Japan,
Dugesia gonocephala exists in both the sexual and asexual forms
(Okugawa, 1953).
Kenk (1941b) grafted the anterior region of a sexual Dugesia tigrina,
containing ovaries and testes, to the posterior region of the asexual form
without genital organs. Several months after the operation, genital
TH. LENDER
studied very extensively and has been well understood since the
investigations of Vandel (1922) on Polycelis cornuta and Planaria
alpina. His paper is a good source of reference to the earlier work.
It is clear that the entire sexual apparatus arises from the differentiation
of the neoblasts. With regard to the genital glands, Dubois (1949)
showed that, after X-irradiation, an ovary is reconstituted from the
neoblasts during regeneration (Fig. 7). The differentiation of the
copulatory apparatus from the neoblasts occurs on the spot without
anatomical relations with the genital glands (Vandel, 1922; Kenk, 1924;
Nobili, 1958). The ducts for conveying the genital products form last.
In Polycelis tenuis, Lender and Le Moigne (1960) distinguish three
phases in the regeneration of the copulatory apparatus (Fig. 8). At the
start, a concentration of neoblasts is visible in the genital region; in the
mass of cells two cavities form which turn into the genital atriums.
During the second stage, a bud differentiates into a penis in the male
atrium and the deferent ducts, as well as the copulatory pouch, are
formed. In the third stage, formation of the penis is completed, the
oviducts become hollow, the deferent ducts continue to progress towards
the testes, and the musculo-glandular organs appear.
Naturally the factors which release this morphogenesis have been
investigated. Vandel (1922) was the first to analyse the determinism of
the regeneration of the genital organs of Polycelis cornuta. He found that
the appearance of the copulatory apparatus was not induced by the
brain or the ovaries. Unfortunately, it is difficult to castrate a planarian
since the testes are situated on each side of the body from the cephalic
region to the level of the genital organs. Vandel caused degeneration of
the testes by raising the temperature of the water in which the planarians
Polycelis cornuta and Planaria vitta were raised, or by introducing a
parasite. Under these conditions the copulatory apparatus did not
regenerate. Vandel, while emphasizing the imperfection of his methods,
postulated that the testes emit substances which cause the differentiation of the genital organs.
But there is another way to attack the problem. One and the same
species may exist in nature in two forms, an asexual form and a sexual
form. Vandel (1925) considered Planaria (Dugesia) subtentaculata of
Southern France to be the asexual form of Dugesia gonocephala. In
America, there is an asexual and a sexual form of Dugesia tigrina
(Planaria maculata) (Kenk, 1937; Hyman, 1939, 1943). In Japan,
Dugesia gonocephala exists in both the sexual and asexual forms
(Okugawa, 1953).
Kenk (1941b) grafted the anterior region of a sexual Dugesia tigrina,
containing ovaries and testes, to the posterior region of the asexual form
without genital organs. Several months after the operation, genital