HOMOLOGIES. 231 



onous, notwithstanding its absolute permanence. 

 In short, drop off the stem of the Crinoid, and 

 depress its calyx to form a flat disk, and we have 

 an Ophiuran ; expand that disk, and let it merge 

 gradually in the arms, and we have a Star-Fish ; 

 draw up the rays of the Star-Fish, and unite 

 them at the tips so as to form a spherical outline, 

 and we have a Sea-Urchin ; stretch out the Sea- 

 Urchin to form a cylinder, and we have a Holo- 

 thurian. 



And now let me ask, Is it my ingenuity that 

 has imposed upon these structures the conclusions 

 I have drawn from them ? have I so combined 

 them in my thought that they have become to 

 me a plastic form, out of which I draw a Crinoid, 

 an Ophiuran, a Star-Fish, a Sea-Urchin, or a 

 Holothurian at will ? or is this structural idea 

 inherent in them all, so that every observer who 

 has a true insight into their organization must 

 find it written there ? Had our scientific results 

 anything to do with our inventive faculties, every 

 naturalist's conclusions would be colored by his 

 individual opinions ; but when we find all zoolo- 

 gists converging more and more towards each 

 other, arriving, as their knowledge increases, at 

 exactly the same views, then we must believe 

 that these structures are the Creative Ideas in 

 living reality. In other words, so far as there is 

 truth in them, our systems are what they are, 



