BIOLOGY 

 LIBRARY 



T AM of course aware of the disadvantages of issuing this 

 *- edition of my Text Book in instalments, and very much 

 regret that this part does not complete the work. The failure 

 to get the whole of the remainder ready has been due to lack, 

 not of will, but of ability and opportunity. 



I take this opportunity of thanking my friend Dr Gowers, for 

 the loan of two woodcuts, as well as for much valuable advice. 

 Throughout the whole of this part I have been largely assisted by 

 my colleague Mr Langley, and by my friend and former pupil 

 Dr Sherrington. The latter, besides helping me with criticisms, 

 has prepared for me most of the figures after original drawings by 

 himself. What little merit there may be in this part is largely 

 due to these two gentlemen. 



M. FOSTER. 



CAMBRIDGE, 



September, 1890. 



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