7. THE LABYRINTH
211
The labyrinth of the lamprey, Lampetra fluuiatilk, has been well
described by de Burlet and Versteegh (1930) and recently by Lowenstein
et al. ( 1968). It is significantly more complex than the labyrinth of Mgxine
(Fig. 1B ) . A unique feature which does not exist in the labyrinth of any
other chordate are two large ciliary sacs forming the center of the cavity
of the membranous labyrinth. Both the anterior and the posterior sac are
further subdivided into upper and lower recesses. They are lined with an
epithelium of large ciliated cells whose long and powerful cilia beat incessantly and create four vortices of endolymph currents of constant direction. Unfortunately, the functional significance of this imposing intralabyrinthine structure is still completely obscure.
Around the ciliary spaces are grouped the various sensory epithelia.
The macula communis still carries a continuous otolithic mass of calcareous crystals. However, its morphological and functional division into
discrete areas is well pronounced and emphasized by the topographic
arrangement of the sensory cells with these. A horizontal anterior macula
area, a medium vertical macula area, and a posterior horizontal macula
area may be held to correspond to the macula utriculi, macula sacculi,
and macula lagenae of the gnathostome labyrinth. There is also an
isolated dorsal patch of sensory epithelium corresponding to the macula
neglecta. There are two ampullae each with a trifid crista and canallike
tubes folded off the dorsal labyrinth cavity. These obviously correspond
to the anterior and posterior vertical canals of the gnathostome labyrinth.
They meet dorsally and their spaces are separated by a valvelike flange
of tissue. There is no crus commune, nor is there a trace of a horizontal
canal. As in Myxine, it can be shown that the cristae of the two vertical
ampullae are capable of monitoring horizontal angular accelerations
( Lowenstein, 1970).
From the elasmobranchs onward the labyrinth carries the full complement of sensory end organs.
Shape, length, diameter, and mutual angle of the semicircular canals
and otolith organs may vary widely, and this variation may be of important functional significance.
C. The Sensory Hair Cell
Recent ultrastructural research has shown that the hair cells of the
end organs of the acousticolateralis system are homologous. They are
always surrounded by a framework of supporting cells, the cell bodies of
which usually lie below the base of the sensory cells to make contact with
the basal membrane of the sensory epithelium. In the fishes, in contrast
to birds and mammals, the sensory hair cells are all of one morphological
211
The labyrinth of the lamprey, Lampetra fluuiatilk, has been well
described by de Burlet and Versteegh (1930) and recently by Lowenstein
et al. ( 1968). It is significantly more complex than the labyrinth of Mgxine
(Fig. 1B ) . A unique feature which does not exist in the labyrinth of any
other chordate are two large ciliary sacs forming the center of the cavity
of the membranous labyrinth. Both the anterior and the posterior sac are
further subdivided into upper and lower recesses. They are lined with an
epithelium of large ciliated cells whose long and powerful cilia beat incessantly and create four vortices of endolymph currents of constant direction. Unfortunately, the functional significance of this imposing intralabyrinthine structure is still completely obscure.
Around the ciliary spaces are grouped the various sensory epithelia.
The macula communis still carries a continuous otolithic mass of calcareous crystals. However, its morphological and functional division into
discrete areas is well pronounced and emphasized by the topographic
arrangement of the sensory cells with these. A horizontal anterior macula
area, a medium vertical macula area, and a posterior horizontal macula
area may be held to correspond to the macula utriculi, macula sacculi,
and macula lagenae of the gnathostome labyrinth. There is also an
isolated dorsal patch of sensory epithelium corresponding to the macula
neglecta. There are two ampullae each with a trifid crista and canallike
tubes folded off the dorsal labyrinth cavity. These obviously correspond
to the anterior and posterior vertical canals of the gnathostome labyrinth.
They meet dorsally and their spaces are separated by a valvelike flange
of tissue. There is no crus commune, nor is there a trace of a horizontal
canal. As in Myxine, it can be shown that the cristae of the two vertical
ampullae are capable of monitoring horizontal angular accelerations
( Lowenstein, 1970).
From the elasmobranchs onward the labyrinth carries the full complement of sensory end organs.
Shape, length, diameter, and mutual angle of the semicircular canals
and otolith organs may vary widely, and this variation may be of important functional significance.
C. The Sensory Hair Cell
Recent ultrastructural research has shown that the hair cells of the
end organs of the acousticolateralis system are homologous. They are
always surrounded by a framework of supporting cells, the cell bodies of
which usually lie below the base of the sensory cells to make contact with
the basal membrane of the sensory epithelium. In the fishes, in contrast
to birds and mammals, the sensory hair cells are all of one morphological