42 INTEODUCTION TO CRYPTOGAMIC BOTANY. 



to seduce an inattentive or ignorant observer into wrong 

 notions as to the relation of the beings between which it 

 exists. Eesemblances of this kind were, at one time, carried 

 to such a point by the Okenists and other German philo- 

 sophical naturahsts, as to involve everything in a cloud of 

 mystical obscurity, like that in which divinity is shrouded by 

 the Hutchinsonians. Homology is of far more value ; for when 

 true it is founded on a deep knowledge of structure, and is 

 indicative either of close or remote relation, while analogy does 

 not necessarily indicate either the one or the other. Affinity 

 expresses the fact that organisms are related, and is of various 

 kinds ; it may be no more than that between one being and 

 another simply as organisms, between the members of distinct 

 divisions, or between those divisions themselves : but when 

 one being, or class of beings, is said to be allied to another, 

 it is generally meant that the peculiarities by which one is 

 distinguished pass gradually into those of the other. It ex- 

 presses immediate relationship and not remote connection. 



29. An excellent view of the relations o f analogy and a ffinity ^^ 

 has been intimated to me in writing by Dr. Hooker. He says, 

 that the difference between analogy and affinity depends 

 mainly on affinity being betrayed by attributes which are 

 as prominent at the earliest period of growth as at the latest, 

 and often more so ; but the contrary holds good of analogy. 

 Thus the hairs of the capitula of Balanophorce, and the para- 

 physes of mosses are perfectly similar, but this circumstance 

 shows no affinity between them, for they are modifications 

 of what are fundamentally different organs. If the first 

 development of the Mammalian ovum be compared with that 

 of an Hcematococcus, it will be impossible to deny the close 

 resemblance, and that both take place on one plan. The 

 relation, then, between the highest Mammal and the obscurest- 

 Alga, though almost infinitely small, yet certain, is capable of 

 being ascertained only in these first stages of development. The 

 relations, again, of plants with central placentation to others 

 with parietal placenta may be obscm-e. Not a trace of the latter 

 structure is to be found in full-grown Gloveworts, or even where 

 the carpels are normally developed. But a monstrous state of 



