97 



Studies in Comparative Physiology. 



1. -observations on the physiology of the 

 fly's intestine. 



By T. Braii.sford Robertson, Ph.D., D.Sc. 



(From the Department of Physiology and Biochemistry, 



University of Adelaide). 



[Read May 13, 1920.] 



Introduction. 



The intestine of an insect represents a rhythmically con- 

 tracting, automatic structure in which the contractile elements 

 are striated muscle fibres (1). In the vertebrates those organs 

 which display similar automaticity and rhythmicity are, with 

 the exception of the heart, smooth-muscle organs. The insect 

 intestine, therefore, affords an opportunity of ascertaining 

 whether the characteristic reactions of sm.ooth and striated 

 muscle to various chemical agents are correlated primarily with 

 their cytological structure or rather with the nature of their 

 functional activity. The single exception afforded by the 

 heart to the rule which prevails in the vertebrata, that 

 automatically contractile organs are provided with smooth 

 muscle, is too isolated and unique to afford a basis for 

 generalization. The functions performed by the heart are 

 peculiar and not paralleled by those performed by any other 

 tissue. We are not surprised to find the striated muscle of the 

 heart differing in many features of its behaviour from the 

 striated skeletal muscles, the more especially since cytological 

 details of its structure also differentiate it from the other 

 striated muscles in the body. In the intestine of the insect, 

 however, we- have an organ performing a strictly analogous 

 function to that which is performed by the intestine of a verte- 

 brate. In the one case the fibres are of tlie striated, in the 

 other of the smooth type. We are led to inquire whether, in 

 their reactions to muscle stimulants or depressants, the striated 

 muscles of the insect intestine resemble the structnraUy similar 

 striated muscles of the vertebrate, or whether they do not, on 

 the contrary, resemble the funclionaJli/ similar smooth muscles 

 of the vertebrates. The experiments herein described were 

 undertaken with a view to throwing some preliminary light 

 upon this question. 



As I have pointed out in a previous communication to this 

 Society (2, 3), if the last abdominal segment of a fly be grasped 

 d2 



