to 4000 A wide. Electrott rnivrogrilphs also show that in the disintegration of morula cells the vesides (vmadophorers of Gansler et ul., 1963)
break free in the tjrst substanw and in some cases are found in association with inicrotibrils thus suggesting t hat there may be a relationship
between fibre prod uctioii and disintqpition of the morula cells. This is
supported by Endean’s ( 1 0 6 5 ~ )
observations that in this species the
morula cell produces fibres when cytolyeed and that fibre production
by CytolysiH cun be obswvccl in I~ibngi~lg drop preparations of blood.
Endean considered tlitit morula wllrs migrate into the test substance
through the walks of the blood vcwels or the mantle. He suggested
that morula cells either directly sttcretc fibres or secrete a material into
the test which then participates in the formation of fibres. This conclusion is supportcd by the fact that, in injured test, morula cells migrate
to and aggregate at the site of injury and wound healing, an obeervation
also made in Halocynthin by Smith (1970a).
Although there is agreement that the morula cells migrate into the
test and arc involved in fibre production, Wardrop (1970) also shows
that the mantle epiderrnis is actively engaged in carbohydrate metabolism. He found that, in animals immersed in a solution of I*Clabelled glucose, the labelled material accumulated in the epithelia of
the mantle and test vessels. Electron-micrographs of t h m epithelia
show that the cells contain extended areas of endoplasmic reticulum
and the Golgi bodios have numerous vesicles. Endean (1961) claimed
that the moruhi cells produced carbohydrate in Phccllwia but this is
not borne out for P p r a by Wardrop’s studies and it seems more likely
that the basic carbohydrate for test synthesis is derived from the
epithelial cells.
(g) Hulocynthiu auruntium (Pallas) (Smith, 1070a, 1970b; 8mith
and Dehnel, 1970) (Fig. 7). The test, of Halocynthia is made up of H,
fibrous matrix but is thinner than in Pyura being only about 1.6 m m
thick. It differs also from many other species by having cuticular
spines on thc surface borne on papillate outgrowths of the test. The
fibres are extmdcd from the tnip of the mantle epidermis cells and
crtalescc to forin t~ laminar structuw just distal to the epidermis in a
region where inoruli~ cells (ferrocytes) are also concentrated. The
laminar struc4iirc of thc test becomes less pronounced toward the
periphery where the fibres extend toward the papillae and where
dispersed vesicular cells are roncentratcd. There irJ therefore a pronounced poirtrization of blood cells in tho terst in which morula cells are
iissociated with it ~ r t t i e
of test foi*matiori and dispersed vesicular cells are
iwsociated with the spiiiouu periphery. Both morula cells and dispersed
vesicular cells iindergo degradntivc c+ha~iges in the test and both typen
break free in the tjrst substanw and in some cases are found in association with inicrotibrils thus suggesting t hat there may be a relationship
between fibre prod uctioii and disintqpition of the morula cells. This is
supported by Endean’s ( 1 0 6 5 ~ )
observations that in this species the
morula cell produces fibres when cytolyeed and that fibre production
by CytolysiH cun be obswvccl in I~ibngi~lg drop preparations of blood.
Endean considered tlitit morula wllrs migrate into the test substance
through the walks of the blood vcwels or the mantle. He suggested
that morula cells either directly sttcretc fibres or secrete a material into
the test which then participates in the formation of fibres. This conclusion is supportcd by the fact that, in injured test, morula cells migrate
to and aggregate at the site of injury and wound healing, an obeervation
also made in Halocynthin by Smith (1970a).
Although there is agreement that the morula cells migrate into the
test and arc involved in fibre production, Wardrop (1970) also shows
that the mantle epiderrnis is actively engaged in carbohydrate metabolism. He found that, in animals immersed in a solution of I*Clabelled glucose, the labelled material accumulated in the epithelia of
the mantle and test vessels. Electron-micrographs of t h m epithelia
show that the cells contain extended areas of endoplasmic reticulum
and the Golgi bodios have numerous vesicles. Endean (1961) claimed
that the moruhi cells produced carbohydrate in Phccllwia but this is
not borne out for P p r a by Wardrop’s studies and it seems more likely
that the basic carbohydrate for test synthesis is derived from the
epithelial cells.
(g) Hulocynthiu auruntium (Pallas) (Smith, 1070a, 1970b; 8mith
and Dehnel, 1970) (Fig. 7). The test, of Halocynthia is made up of H,
fibrous matrix but is thinner than in Pyura being only about 1.6 m m
thick. It differs also from many other species by having cuticular
spines on thc surface borne on papillate outgrowths of the test. The
fibres are extmdcd from the tnip of the mantle epidermis cells and
crtalescc to forin t~ laminar structuw just distal to the epidermis in a
region where inoruli~ cells (ferrocytes) are also concentrated. The
laminar struc4iirc of thc test becomes less pronounced toward the
periphery where the fibres extend toward the papillae and where
dispersed vesicular cells are roncentratcd. There irJ therefore a pronounced poirtrization of blood cells in tho terst in which morula cells are
iissociated with it ~ r t t i e
of test foi*matiori and dispersed vesicular cells are
iwsociated with the spiiiouu periphery. Both morula cells and dispersed
vesicular cells iindergo degradntivc c+ha~iges in the test and both typen