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to the disease called rickets, that is prevalent among human 

 beings under corresponding circumstances. 



Lastly, varieties of texture : these are generally the direct 

 result of physical conditions, and have no very great import- 

 ance ; shells found in limestone districts are for instance 

 thicker than those on other soils, on the average. Some, 

 from their inability to procure or assimilate carbonate of lime, 

 will be thin, fragile, and almost membranous ; and like results 

 arise in other animals from similar causes. One word at the 

 end in defence of the much-abused varietal names. I would 

 not hesitate to apply a name to any variety of sufficient 

 distinctness to be recognised, nor do I quite understand why 

 one should not do so. People say, how shall we remember 

 all these names ? — but what they mean is, I won't bother to 

 study the characters of these varieties ; for you may be sure 

 that they could not get on without the names if they wished 

 to speak and write of varities. Take our own species, in 

 which we have actually named every individual ! isn't that 

 horrible — what a Jiost of names — how are we to remember 

 them ? Well, we remember those we like, and for the rest, 

 their names serve as a surer means of finding them than any 

 description. If you ask me to find you Ebenezer McNabbles, 

 I look him up in the directory, which corresponds to a hand 

 list of species and varieties, and probably enough I find him ; 

 but, if you tell me of a tall man, with a long beard, short 

 hair, green eyes, a pimple on his nose, and so on, I am likely 

 to wander about some time and make many enquiries before 

 I come across him, if I do so at all. So it is with varieties ; 

 one can remember a variety once seen, and associate it with 

 a certain name — and others can do the same ; but the imper- 

 fections of language are far too great to make it convenient 

 or even possible to go on the principle of describing a thing 

 every time it is mentioned, not to speak of the waste of time 

 and space in so doing. 



Now I have finished. The subject is so extensive that I 

 have been able only to skim over the surface of a few aspects 

 of it, and touch upon one or two questions that had presented 

 themselves to me. I look forward to the light that you, who 



