CLASSIFICATION OF ANIMALS 



Exercise 1. — Examination of Representative Forms. 



(a) A sufficient number of representative animals has now been 

 studied in detail to enable you to understand the typical modifications 

 of structure as related to function in existing animals. Remember 

 that although types of structure are varied, animals are essentially 

 similar in their fundamental capacities. In your study of museum 

 and other specimens as outlined below, you should keep in mind that 

 structure is meaningless unless seen in its relation to function. Com- 

 plexity of structure is correlated with increased number of cells, their 

 relative location, and their specialization. The term phylum is ap- 

 plied to certain larger groups of animals, the members of which carry 

 on their activities by means of similar structures. 



(b) Phylum Protozoa. — The forms studied. Amoeba, Paramecium, 

 and Euglena, together with figures and demonstrations of other forms, 

 sufficiently illustrate this phylum. The distinguishing characteristic 

 is the unicellular state. 



(c) Phylum Porifera. — Examine simple sponges such as Scypha 

 (Grantia) and Leucosolenia. Note the osculum, or exhalant opening, 

 and many small incurrent pores on the surface. The structure of 

 larger sponges, such as the bath sponge and others, may be compared 

 with that of the simpler types in terms of budding, folding, and 

 vegetative growth (c/. Fig. 41, p. 84). Distinguishing characteristics 

 of the phylum are: absence of a digestive cavity comparable to that 

 of other Metazoa; attachment during the adult stage; absence of 

 organs and true tissues, although there is a limited amount of cell 

 specialization; a skeleton of fibers or spicules. The sponges are the 

 simplest of the many-celled animals, with the exception of the small 

 group known as Mesozoa which is sometimes called a phylum. 



(d) Phylum Ccelenterata. — The examples studied are hydras and 

 the hydroids with their medusae or jellyfishes. Examine other repre- 

 sentatives, such as the larger jellyfishes, sea-pens, sea-fans, sea-anem- 

 ones, corals, and ctenophores. Understand the relation between soft 

 parts and skeletons. Distinguishing characteristics are: some degree 

 of cell specialization and division of labor but no true tissues; radial 

 symmetry; a single opening to the digestive cavity; two germ layers, 



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