THE 



PHYSIOLOGY OF THE INVERTEBRATA. 



CHAPTER I. 



1 N T K O D U C T I O N. 



Ammal pliyaioloiji/ may be defined as that braucli of biology 

 whicli is concerned in the elucidation of the various functions 

 which take place in the animal economy. It is a branch of 

 study quite distinct from morphology, chorology, and setio- 

 logy ; and as a separate branch of biological science we propose 

 to treat it in the following pages. 



Researches undertaken to investigate accurately the proper 

 physiological functions of the various organs and tissues of 

 the Iiirirtrhrata were greatly needed; and it is only during 

 the last few years that certain biological chemists — fully 

 equipped with the necessary manipulative skill — have con- 

 siderably advanced this important but much-neglected branch 

 of biolog}-. 



If one studies any particular organ from only one aspect, 

 incomplete or erroneous conclusions are apt to be drawn. 

 For instance, the vesicular tissue lying in the rectal loop in 

 A.sculia, and in some species extending over the intestine, is 

 well known to be renal in function. This vesicular tissue is 

 a true kidney pliyHiolonimJhi ; riwrpholofiically it is another 



A 



