2. CHITIN AND MUCOSUBSTANCES
97
green algae (Chlorophyceae). Elsewhere, in plants, cellulose provides
the principal mechanical support. All fungi, with the exception of Oomycetaceae, Monoblepharideae, and Laboulbeniales contain chitin. By X-ray
diffraction methods, chitin from the sporangiophores of Phycomyces
blakesleeanus displayed a structure closely similar to that of the crustacean Palinurus vulgaris. In general, fungal chitin appears to be identical
with that isolated from Crustacea; like cuticular chitin, it has been found
in highly oriented molecular forms. In view of the close molecular similarity of chitin and cellulose at the macromolecular level, it is tempting
to consider them as biological alternatives, as for instance for the phylogenetic classification of related groups, particularly of fungi
(33).
Actinomyces nocardia, and species of Streptomyces and Micromonosperma are all devoid of both chitin and cellulose and may be thus
considered to be more closely related to bacteria than to fungi.
Chitin in small amounts has been reported in the cell wall of many
species of yeast (34, 35) and in Nadsonia fulvescens, Rhodotorula glutinis, and Sporobolomyces roseus, where it comprises about 10% of the
walls (36).
The amount of chitin in fungal walls varies between traces and
50-60% of the dry weight. In the mushroom a yield of 35% chitin was
obtained, and its identity was confirmed by X-ray diffraction. As in
cuticle, fungal chitin is associated with other substances, mainly carbohydrate, in the cell walls.
General reviews of fungal chitin have been compiled by Tracey (37)
and by Foster and Stacey (38).
C. IN ANIMALS
Chitin is commonly found in the supporting tissues of invertebrate
animals; it is rarely found in chordates. It can occur both as "soft" chitin
(as in wing hinges of locusts) or, as in arthropod cuticle, hardened by
mineralization or sclerotization. In either form it is found mostly in
invertebrate exoskeletons, and in tendons, gut lining, and egg shells.
Chitin is absent from all Protozoa and, in general, from Porifera,
though it is reported in the gemmules of the freshwater sponge
Spongilfa. Among Coelenterata, it is reported from the perisarc of
hydromedusae (even from the fossil Graptozoa). Genera without a perisarc, on the other hand, do not give reactions of chitinous material. It
has not yet been detected in Ctenophora, nor is it known from the body
covering of flatworms (Platyhelminthes), roundworms (Nematoda), nor
Acanthocephala, but it occurs in their egg shells. There are no reports
of chitin from the body walls of annelid worms, but it does occur in jaws,
gut lining, and setae. In the Mollusca, chitin occurs in the internal skele-
97
green algae (Chlorophyceae). Elsewhere, in plants, cellulose provides
the principal mechanical support. All fungi, with the exception of Oomycetaceae, Monoblepharideae, and Laboulbeniales contain chitin. By X-ray
diffraction methods, chitin from the sporangiophores of Phycomyces
blakesleeanus displayed a structure closely similar to that of the crustacean Palinurus vulgaris. In general, fungal chitin appears to be identical
with that isolated from Crustacea; like cuticular chitin, it has been found
in highly oriented molecular forms. In view of the close molecular similarity of chitin and cellulose at the macromolecular level, it is tempting
to consider them as biological alternatives, as for instance for the phylogenetic classification of related groups, particularly of fungi
(33).
Actinomyces nocardia, and species of Streptomyces and Micromonosperma are all devoid of both chitin and cellulose and may be thus
considered to be more closely related to bacteria than to fungi.
Chitin in small amounts has been reported in the cell wall of many
species of yeast (34, 35) and in Nadsonia fulvescens, Rhodotorula glutinis, and Sporobolomyces roseus, where it comprises about 10% of the
walls (36).
The amount of chitin in fungal walls varies between traces and
50-60% of the dry weight. In the mushroom a yield of 35% chitin was
obtained, and its identity was confirmed by X-ray diffraction. As in
cuticle, fungal chitin is associated with other substances, mainly carbohydrate, in the cell walls.
General reviews of fungal chitin have been compiled by Tracey (37)
and by Foster and Stacey (38).
C. IN ANIMALS
Chitin is commonly found in the supporting tissues of invertebrate
animals; it is rarely found in chordates. It can occur both as "soft" chitin
(as in wing hinges of locusts) or, as in arthropod cuticle, hardened by
mineralization or sclerotization. In either form it is found mostly in
invertebrate exoskeletons, and in tendons, gut lining, and egg shells.
Chitin is absent from all Protozoa and, in general, from Porifera,
though it is reported in the gemmules of the freshwater sponge
Spongilfa. Among Coelenterata, it is reported from the perisarc of
hydromedusae (even from the fossil Graptozoa). Genera without a perisarc, on the other hand, do not give reactions of chitinous material. It
has not yet been detected in Ctenophora, nor is it known from the body
covering of flatworms (Platyhelminthes), roundworms (Nematoda), nor
Acanthocephala, but it occurs in their egg shells. There are no reports
of chitin from the body walls of annelid worms, but it does occur in jaws,
gut lining, and setae. In the Mollusca, chitin occurs in the internal skele-