136 



ON THE COKPUSCLES OF CEKTAIN MAEINE 



WOKMS. 



By Lionel J. Picton, B.A. 



[Read Dec. 10th, 1897.] 



"With Plate IX. 



In comparing simple organisms with higher animals, a 

 part is often remarked with a common origin and similar 

 function in both, but relatively much better developed in 

 the so-called "low" animal than in the higher. Three 

 quarters of the bulk of a Tunicate, for instance, may 

 consist of the walls of the pharynx only ; again in certain 

 Crustacea, the eyes may occupy a third of the body. It 

 is quite evident, in such cases, that the parts in question, 

 pharynx or eyes, as the case may be, are of much greater 

 importance to the Tunicates, or Crustacea, than the 

 corresponding organs in ourselves, for instance, are to us. 



The subject with which I am to deal is a similar case. 

 The primitive body cavity in a healthy mammal is a 

 cavity only in name. I need not remind you that the 

 fluid which is contained in it is normally very small. It 

 has collapsed, like that of a bag emptied of its contents, 

 to use the familiar explanation, and the little fluid that 

 remains just suffices to moisten the adjacent surfaces. If 

 there be more fluid, then, of course, we have a pathological 

 condition, as in pleurisy. 



In many invertebrata, however, the coelom is large and 

 open, and filled with a corpusculated fluid, Differences, 



