1881 KESEAKCH ON ECHINODEKMS 107 



page 167, I have a good sentence about a man 

 finding two vars. of Lythrum, and testing them by 

 fertility, and coming to egregiously wrong conclu- 

 sion. 



I think your idea of reference to best books and 

 short history of subject good. By the way, you have 

 made me quite proud of my chapter on Hybridism, I 

 had utterly forgotten how good it appears when dressed 

 up in your article. Yours very sincerely, 



CHAKLES DAKWIN. 



I have had a hunt and found my little article on 

 Geese, which please hereafter return. 







To C. Darwin, Esq. 



18 Cornwall Terrace : November 18, 1880. 



Yery many thanks for your kind assistance and 

 expressions of approval. It was stupid of me to for- 

 get your article in l Nature ' about the geese. I now 

 quite well remember reading it when it came out. 



Focke's book is just the very thing I wanted, as 

 it supplies such a complete history of the subject. If 

 I do not hear from you again, I shall keep it for a 

 few days to refer to when the proof which I have 

 sent to press shall be returned with my historical 

 sketch added. 



I have now nearly finished my paper on the 

 physiology of the locomotor system in Echinoderms. 

 The most important result in it is the proof, both 

 morphological and physiological, of a nervous plexus, 

 external to everything, which in Echinus serves 



