CHAPTER XXV. 



EXERCISES IN COMPARATIVE PHYSIOLOGY, MORPHOLOGY, 

 AND ECOLOGY. 



455. Now that the student has studied in some detail the 

 work which even the simplest organisms must perform, the 

 organs by means of which this necessary work is done in some 

 of the principal types, and the relations which animals assume 

 to each other and to the environment in general, it is desirable 

 that he should bring these facts into such relations that they 

 may be compared. The likenesses, the unlikenesses, and the 

 progressive differentiation are thus brought into clear relief. 

 The following outline exercises are intended to guide the stu- 

 dent in this task. They are by no means exhaustive, but will 

 suggest the principal points most essential to such a resume. 

 The laboratory notes, the text-book, and all the reference books 

 at his command, should be used by the student. The teacher 

 should require the student to be able to cite his authority for 

 all important statements not his own and, if possible, require 

 corroboration by reference to more than one authority. The 

 author has found that tables with parallel columns such as 

 those on pages 340 and 343 furnish an economical and other- 

 wise satisfactory mode of displaying the results of these studies. 



I. Fundamental Form (Promorphology). Indicate for 

 each of the important phyla, or for chosen representatives of 

 them, the following matters of general form: kind of sym- 

 metry represented and the perfection of its development; the 

 degree and character of segmentation ; the position, number, 

 character, and arrangement of the appendages; the external 

 and the internal evidences of cephalization ; the relation of the 

 principal organs of the animal to the horizontal and vertical 

 planes. 



II. Physiology and Morphology. Compare the mode of 



