INTEODUCTION TO CRYPTOGAMIC BOTANY. 39 



quently confounded by the student. Analogy, in the first 

 place, indicates certain resemblances between things, whether 

 similar or dissimilar in nature. A large portion of poetical 

 images are derived from such resemblances. These may be 

 more or less remote. The old Pythagorean notion, for instance, 

 that an egg is a microcosm representative of the earth, in which 

 the shell answers to the earth, the white to water, the yolk to 

 fire, and the bubble of air at the end to the atmosphere, is a 

 case of very remote analogy. The notion, again, of the elder 

 Agardh that a bird is an analogue of the world (like it, it 

 moves freely through space ; the feathers are the trees which 

 grow out of it, and the parasites amongst the feathers the 

 animals which move amongst the trees), is a case of rather 

 closer analogy than the former, but still very remote and 

 fanciful. There is not a particle of affinity, of course, in 

 either case. Analogy, however, may exist between things 

 which have a closer relation to each other The wings of an 

 insect, for instance, have a certain resemblance to the wings of 

 a bird ; their function is the same, but they are not modifi- 

 cations of the same organ.* The tracheae of insects, again, 

 have the same function, in all probability, as the spiral vas- 

 cular tissue of plants ; but they can scarcely be said to be the 

 same organ. The fovilla of the pollen tubes of Pheenogams 

 has the same function as the spermatozoids of Cryptogams, 

 but they are not the same organ. These, then, are so many 

 cases of likeness of function, without any similarity of origin 

 or essence, and they are, therefore, cases of analogy, and the 

 objects themselves are called analogues of each other. There 

 are likenesses, too, where there is neither identity of origin nor 

 function. Such likenesses may be general resemblances, as 

 that of certain galls to Fungi. The one are sometimes exact 

 counterparts of the other, but the resemblance begins and ends 

 there, and leads to no important conclusions. Exactly in the 

 same way there may be two extensive genera, not in the least 



* The palpi of spiders have, in all prohability, the same general 

 functions with those of insects, but there is a generative function 

 superadded. In one sense, then, they are homologues, in another, 

 analogues. 



