CLASSIFICATION OF ANIMALS 173 



individuals called zooids. Some colonies have highly specialized pro- 

 tective members in the form of avicularia which are beaklike, or 

 vibracula which are whiplike. The zooids feed by means of ciliated 

 tentacles. The fresh-water representatives commonly reproduce by 

 internal buds, called statoblasts. Distinguishing characteristics of 

 the phylum are: mouth surrounded by tentacles, digestive tract 

 U-shaped, and with anal opening; three germ layers; coelom within 

 which germ cells are formed; a ganglion between mouth and anus, 

 but no special nervous sj'stem or sense organs; skeletal secretion by 

 ectoderm often conspicuous; mostly colonial. 



(j) Phylum Brachiopoda. — Demonstrations of brachiopods, or 

 lamp-shells, such as Lingula and Terebratulina, should be examined. 

 You may be familiar with brachiopod shells as fossils, since these are 

 abundant in many localities. The shells are paired dorso-ventrally, 

 not right and left as in a clam, and the animal is attached by a stalk. 

 Internally the most conspicuous feature is a feeding organ called the 

 lophophore which occupies a large part of the space within the shells. 

 Refer to figures and understand such details of the internal structure 

 as time and material permit. Distinguishing features are: bilateral 

 symmetry as shown by the characteristic dorso-ventral shells and 

 stalk; short digestive tract with mouth and anus; three germ layers; 

 a body cavity ; a pair of nephridia ; the lophophore. 



(k) Phylum Rotatoria. — The rotifers, or wheel animalcules, are 

 forms of microscopic size occurring principally in fresh water. They 

 are often found in cultures and you may have seen many of them 

 in studying Protozoa. Most genera are free-swimming; some are ses- 

 sile; others live in tubes. Examine material from cultures rich in 

 rotifers. Why were they called "wheel animalcules" by the early 

 naturalists? Are the rotifers you have for study bilaterally sym- 

 metrical? Is the body obviously divisible into head, trunk, and tail 

 regions? Can the animal become attached? How does the animal 

 move and feed? A non-cellular cuticle is present in all rotifers, and 

 in some genera this cuticle is heavy enough to be called a shell, or 

 test. The corona, or ciliated region about the mouth, may be lobed 

 or consist of a single circlet of cilia. The digestive tract includes: a 

 pharynx, containing a "milling" organ called the mastax; a stomach; 

 and an intestine. The anus is non-functional in some species. Under- 

 stand the foregoing parts and the nervous, excretory, and reproductive 

 systems, as they may be identified in the species available. Note 

 species with degenerate males; and the life-cycle with respect to the 

 two kinds of eggs. Understand the possible significance of the rotifer 

 type of structure in the evolution of invertebrates. Distinguishing 



