INTRODUCTION. 



XXXI 



larval stage. In the younger form (Fig. 7) it is rudi- 

 mentary, but scarcely more so than in Mcera (Fig. 8). 



Fig. 6. 



Immediately posterior to the point of attachment of this 

 organ with the alimentary canal are a series of muscular 

 bands lying transversely across the latter, which probably 

 fulfil the office of sphincter muscles by compressing the 

 passage just posteriorly to the efferent orifice of this sup- 

 posed urinary organ. Muscles very similar in appearance 

 are situated near the terminal exit of the alimentary tube, 

 and probably fulfil the office of sphincter muscles to the 

 anal outlet. 



The contents of the appendage that we call the urinary 

 organ are, under an object-glass of one-fifth focus, 

 resolved into small round cells, containing a granular 

 nucleus (Fig. 9). These cells arc closely packed together, 



Fig. 7. 



Fig. 8. 



but not so as to lose their rounded character, and the 

 whole are confined within stout walls. 



