118 F. H. STEWART. 



certain resemblance to a coagulated albuminous fluids but it 

 should be contrasted with, e. g., the ccBlomic fluid of annelids, 

 as seen in section. The latter, if stained with nigrosiu, 

 appears as an exceedingly loose reticulum of very fine fibrils, 

 which do not stain very intensely ; the former, in some 

 places, shows a very fine fibrillation, with a homogeneous back- 

 ground, in others stains intensely and evenly. I would not, 

 however, lay much stress on this, since I know of no test 

 which would enable us with the microscope to differentiate a 

 coagulum from a lowly organised jelly. On the other hand, 

 a coagulum formed in a fluid ought to contract, and not com- 

 pletely fill the space occupied by the fluid ; the substance in 

 question completely fills the space, while the thickness of the 

 walls lining the space forbids the idea that they might have 

 contracted on a loose coagulum. 



The presence of nuclei and their character is the strongest 

 argument in favour of the third view. Any nuclei occurring 

 in a fluid must belong to floajting cells. Such cells would 

 probably be amoeboid, and would almost certainly have a 

 reasonable amount of protoplasm and definite cell outlines. 

 The nuclei which I have found, on the contrary, are either 

 entirely naked or have a very fine pellicle of protoplasm, 

 which shades off into the surrounding matrix. This, I think, 

 suggests that they are connective-tissue nuclei rather than 

 the nuclei of wandering cells. They are also identical with 

 the nuclei of the stroma in the oesophageal region. 



For these reasons I would put forward the view that the 

 body cavity is filled by a mesenchyne, which in the oeso- 

 phageal region takes the form of a nucleated fibrillar net- 

 work in the regions behind the oesophagus of a jelly-like 

 substance, also nucleated. The reason for the difference in 

 character of the tissue in the oesophageal and other regions 

 is, that in the former it has a special function, which 1 have 

 explained above. At the same time, I put this view forward 

 only tentatively. It would be rash to speak dogmatically on 

 so important a point without having thoroughly investigated 

 a number of allied forma. 



