40 INTRODUCTION TO CRYPTOGAMIC BOTANY. 



related to each other, in which striking resemblances may exist 

 between certain species of two or more series. Such resem- 

 blances may be purely accidental, or they may be part of that 

 harmony of the works of Creation, in which certain likenesses 

 seem to blend the most dissimilar organisms into one connected 

 mass ; "a mighty maze! but not without a plan." No one sup- 

 poses, for instance, that there is any relation between those twig- 

 like caterpillars which deceive their enemies, or the leaf-like 

 wings of the Mantis, and the objects which they resemble. 

 These examples are, in a lower sense, cases of analogy; but, in 

 a higher sense, we understand by analogy those cases in which 

 organs have identity of function, but not identity of essence or 

 origin. 



26. In deeply studying the relations of organised beings, it 

 is necessary to study the changes which the same organ under- 

 goes in different individuals. Such considerations constitute 

 what is called morphology. The organ itself may, evidently 

 be the same, and yet the functions of it may be wholly 

 different. If, for instance, we study the mode in which pollen 

 grains are developed within the mother-cells, and compare it 

 with the development of the spores in the higher Cryptogams, 

 there cannot be a doubt that the organs are similar in origin, 

 though the functions are totally different. The spores germinate 

 in precisely the same manner as the pollen grains, and, in some 

 cases, from definite points; the end of this germination is, how- 

 ever, totally different ; in one case it is the growth of the new 

 individual, in the other case the impregnation of a cell. Such 

 bodies, then, are homologous ; they are identical in essence 

 and origin, but dissimilar in function.* The spores of the 

 Cryptogam, on the other hand, and the seed of a Phcenogam, 

 have, to a certain extent, the same function, but they have no 

 resemblance of essence or origin ; they are, therefore, analogous, 

 and not homologous. These distinctions, when once fairly 

 grasped, are of immense importance in estimating the rela- 



* The primary spores of such parasitic Fungi as are represented, fig. 

 6, originate in a totally different way from the spores of the higher 

 Cryptogams, and though they germinate at definite points, can be only 

 considered as analogues of pollen grains. 



