228 SCIENTIST IN RUSSIA The role of the mollusc in sedimentary rock formation. Mollusc fossils (Ammonites and Belemnites). Laboratory work: Acquaintance with the external appearance and dissection of the mussel. Demonstration of living molluscs, specimens and diagrams. V. Phylum Arthropoda (19 hours) Cray-fish as the representative of the phylum Arthropoda; its external and internal structure related to the way of life. The more complex organisation as compared with the hookworm. The chitinous shell and segmented limbs as the characteristic of the crustaceans. Division of the phylum into classes. General characteristic of the class Crustaceans. The significance of the lower Crustaceans (Daphrtia and Cyclops) in the fishing industry. The most important characteristic peculiarities of the class Arachnida and Myriapoda. Class Insecta. External and internal structure of insects. Peculi- arities of reproduction and development; insects with complete and incomplete metamorphosis. Representatives of the most important groups of insects (external structure, way of life, diversity of adapting devices, practical signi- ficance, and method of combating pests): locusts as representative or the Orthoptera, parasitic lady-bird and bed-bug as representative of Hemiptera; cabbage-moth, silkworm as representatives of Lepidoptera,. and the may-beetle as a representative of Coleoptera; house-fly and mosquito as representative of Diptera, the bee and the ant as repre- sentatives of Hymenoptera. Points of similarity between Arthropoda and hook-worms. Laboratory work: (a) External examination and dissection of crayfish or a large* insect (e.g., cockroach). (6) Acquaintance with representatives of the various types of. insects (specimens). Demonstration : (a) Structure of crayfish or insect (diagrams)* (£) Representatives of the Arachnida and Myriapoda (specimens*, diagrams), (c) Variation of form and specialised devices of insects (living, specimens, collections, diagrams). (