PROMORPHOL OOT. 133 



IV. PROMORPHOLOGY, OR STUDY OF THE FUNDAMENTAL FORMS. 



Organic and Inorganic Bodies. The structure of the individual 

 animal rests upon the regular combination of differently-function- 

 ing organs. The organs thus assume a relation to one another 

 which is definite for each animal group, or varies only in subordi- 

 nate ways. If the various groups be compared with reference to 

 the principle of the arrangement of parts, there appear a few 

 fundamental forms which play a role in morphology similar to that 

 of the fundamental forms of crystals in mineralogy. But we must 

 not carry this comparison too far, and attempt to compare the 

 study of the fundamental forms, the promorphology, of animals 



FIG. 84. Spongilla fluriatilis, fresh-water sponge. (After Huxle 

 with dermal pores; be, region of the ampullae; c/, 



(After Huxley.) a, superficial layer 



osculum. 



with crystallography as of equal value. A crystal is a mass made 

 up of similar parts; its form is the necessary and immediate result 

 of the chemico-physical constitution of its molecules. A direct 

 connection of this kind between molecular structure and funda- 

 mental form does not, and cannot, exist in the organism, since 

 each organ is composed of many chemical combinations. Conse- 

 quently there is lacking also the mathematical regularity which 

 occurs in crystals. Even in the case of animals which have the 

 greatest regularity in the arrangement of their parts there is not 

 an entire conformity to the demands of the fundamental form, so> 

 that we are compelled to ignore certain greater or less variations. 

 If, for example, we call man bilaterally symmetrical, we overlook 

 not only the slight asymmetry of a nose awry, etc., but also what 

 is more important that the liver has been pushed to the right, 



