Exercises XII and XIII 



PLANT AND ANIMAL CLASSIFICATION 65 



from it an internal space lined by ectoderm and 

 endoderm. The higher phyla all possess a true 

 coelom. 



In the protostomes, the mesoderm is formed 

 by cells which wander in from the ectoderm and 

 bud off the endoderm to form a solid layer, in 

 which the cavity later develops that becomes the 

 coelom. In the deuterostomes, the mesoderm is 

 formed by outpocketings of the endoderm to 

 form hollow pouches, the cavity of which is the 

 coelom. 



WORK ASSIGNMENT 



These two laboratory sessions will be devoted 

 to a study of the diversity of organisms, animal 

 and plant. Representative plants and animals 

 of all the major groups will be on display, and 

 the student should study each of them carefully. 

 There will also be a group of unlabeled plants 

 and animals to examine and to compare with the 

 labeled specimens. 



Working independently, place the unlabeled 

 organisms within their major categories: phyla 

 for the most part; but also subphyla among the 

 vascular plants, and classes among the Pterop- 

 sids; similarly, classes among two of the animal 

 phyla, the Arthropods and Chordates. In a few 

 sentences and perhaps a sketch, defend each of 

 your identifications. Hand in your results at 

 the end of the period. 



To prepare for these laboratory sessions, and 

 to supplement them, students should, if possible, 

 spend two or three hours in the nearest accessi- 

 ble museum that has a display of representative 

 organisms of the major plant and animal phyla. 

 For such an excursion to be meaningful, the 

 student should first abstract the pertinent ma- 

 terial from our list of readings, and probably 

 have with him the charts that appear in this 

 manual, as well as the outline that follows. 

 Notes should be taken about the phyla observed, 

 their distinctive characteristics, the range of 

 organisms they include, and the relationships 

 among them. 



A Short Guide to 

 Plant and Animal Classification 



During the year a variety of organisms will be 

 used in the laboratory. It will be worth while to 

 attempt to classify them. As an aid in doing this, 

 an abbreviated guide is included here. Various 

 authors disagree on minor points of classifica- 

 tion, but practically any textbook of botany or 

 zoology can be consulted for more details. 



PLANT KINGDOM* 



Plants are usually considered as organisms 

 with stiff cell walls and with chlorophyll. 



* Adapted from C. A. Villee, Jr., Biology, 4th ed., 

 Saunders, 1962. 



Subkingdom Thallophyta (Gr. thallos, young 

 shoot; phyton, plant). Plants not forming em- 

 bryos. These are the simplest plants without true 

 roots, stems, or leaves; there is little differentia- 

 tion of tissues. 



1. PHYLUM CYANOPHYTA (or Myxophyta) (Gr. 

 myxa, mucus; phyton, plant). The blue-green 

 algae. Chloroplasts and nuclei not distinct. 



2. PHYLUM EUGLENOPHYTA (Gr. eu, Well, truc; 

 glene, pupil of the eye or socket of a joint). The 

 Euglenoids. 



3. PHYLUM CHLOROPHYTA (Gr. chloros, green; 

 phyton, plant). The green algae. Contain dis- 

 tinct nuclei and chloroplasts. Spirogyra and 

 Oedogonium. 



