SOME ASPECTS O F THE BlOLOGY O F THE CHAETOGNATHS
283
have a globe-like shape and are richer in cytoplasm while the latter are
smaller and their nuclei are reduced. The “ corona ” in Spadella has
been re-examined in fuller detail by Reisinger (1934) who, like Grassi,
recognized two distinct regions, the inner corona and the outer corona.
I n the middle regions, between the two rings of cells, there is a thin
annular canal, destined to gather the products of excretion. I n the
inner ring there are only glandular cells which have a pear-like shape
and whose thinner extremity looks towards the annular canal. The
cells of the outer ring are smaller with generally pycnotic nuclei and
are provided with vibratile cilia which, according to Reisinger, should
have a motor function. The majority of authors believe that the
ciliated ring has a sensory function, tactile according to Grassi, John
and Parry or olfa,ctory according to Hertwig. John (1933) tested the
sensitive reactions of the different parts of the body in Xpadella by
directing a small jet of water on to the surface of the animal ; he found
that the animal endeavours to shift its position only when the jet is
directed on the “ corona ciliata ”. Reisinger, previously, considers it to
be an excretory organ and comes to this conclusion not only on
morphological grounds, but based also on the results of experiments
made with vital stains. The ciliary loop would, therefore, in his opinion
be an organ similar to a solenocytic protonephridium. More recently he
has been modifying some of his conclusions and has confirmed some of
my results (Ghirardelli, 1959e). A new work by Reisinger “Ultrastrukturforschung und Evolution ” is to be published in “ Physicomedica ” Wurzburg (Reisinger, personal communication).
Before concluding, I shall briefly summarize some results of my
own researches on the ciliated ring (Ghirardelli, 1958b, 1959e).
I n Xpadella cephaloptera the cells of the “ corona ciliata ” are
certainly of ectodermal origin, like those of the ventral ganglion, from
which in the first 2 weeks of life they cannot be distinguished by their
morphological characters. Furthermore, in the larvae, for about 15
days, the primordium of the ring and that of the ganglion are intimately
connected so that the lateral-posterior regions of the former run
without interruption into the anterior part of the latter. These anlagen
are already present at hatching : that of the future ventral ganglion
shows relative dimensions distinctly larger than in adult animals and
has not yet reached its final ventral position but consists of two largc
masses of cells placed a t the sides of the body and extending along the
whole length of the trunk. Two days later the corona ciliata placed
directly beneath the single layered epidermis forms an annular strip of
much thickened cells, except in the inside of the strip where, starting
from the fourteenth day a canal appears which runs through it. At
283
have a globe-like shape and are richer in cytoplasm while the latter are
smaller and their nuclei are reduced. The “ corona ” in Spadella has
been re-examined in fuller detail by Reisinger (1934) who, like Grassi,
recognized two distinct regions, the inner corona and the outer corona.
I n the middle regions, between the two rings of cells, there is a thin
annular canal, destined to gather the products of excretion. I n the
inner ring there are only glandular cells which have a pear-like shape
and whose thinner extremity looks towards the annular canal. The
cells of the outer ring are smaller with generally pycnotic nuclei and
are provided with vibratile cilia which, according to Reisinger, should
have a motor function. The majority of authors believe that the
ciliated ring has a sensory function, tactile according to Grassi, John
and Parry or olfa,ctory according to Hertwig. John (1933) tested the
sensitive reactions of the different parts of the body in Xpadella by
directing a small jet of water on to the surface of the animal ; he found
that the animal endeavours to shift its position only when the jet is
directed on the “ corona ciliata ”. Reisinger, previously, considers it to
be an excretory organ and comes to this conclusion not only on
morphological grounds, but based also on the results of experiments
made with vital stains. The ciliary loop would, therefore, in his opinion
be an organ similar to a solenocytic protonephridium. More recently he
has been modifying some of his conclusions and has confirmed some of
my results (Ghirardelli, 1959e). A new work by Reisinger “Ultrastrukturforschung und Evolution ” is to be published in “ Physicomedica ” Wurzburg (Reisinger, personal communication).
Before concluding, I shall briefly summarize some results of my
own researches on the ciliated ring (Ghirardelli, 1958b, 1959e).
I n Xpadella cephaloptera the cells of the “ corona ciliata ” are
certainly of ectodermal origin, like those of the ventral ganglion, from
which in the first 2 weeks of life they cannot be distinguished by their
morphological characters. Furthermore, in the larvae, for about 15
days, the primordium of the ring and that of the ganglion are intimately
connected so that the lateral-posterior regions of the former run
without interruption into the anterior part of the latter. These anlagen
are already present at hatching : that of the future ventral ganglion
shows relative dimensions distinctly larger than in adult animals and
has not yet reached its final ventral position but consists of two largc
masses of cells placed a t the sides of the body and extending along the
whole length of the trunk. Two days later the corona ciliata placed
directly beneath the single layered epidermis forms an annular strip of
much thickened cells, except in the inside of the strip where, starting
from the fourteenth day a canal appears which runs through it. At