284 LIONEL JAMES PTCTON. 



places in contact, yet a considerable space is generally left 

 between them (fig. 23). This lumen appears so constantly 

 that I think it is natural, and not due to fixation and handling, 

 nor has it the appearance of an artefact. Moreover it is pos- 

 sible in a fresh specimen to snip the heart longitudinally with 

 a pair of fine scissors, so as partially to slit open the heart- 

 body, so that on microscopic examination a single thickness of 

 the wall is viewed. If this be really the case, as I suppose, 

 then the lumen is probably greater in life than it appears in 

 sections. There is another even more important discrepancy 

 between the descriptions of different naturalists. Whilst 

 Jourdan speaks of the lumen as " communiquant avec le tube 

 digestif," Bles (5), on the contrary, states that it has no con- 

 nection, not even contact, with the gut. As a matter of fact, 

 a series of sections clearly shows that in its posterior part it is 

 attached to the gut, and that this connection extends for a con- 

 siderable distance; on the other hand, no open duct or pas- 

 sage from the one into the other is seen to pierce the gut-wall. 

 The attachments to the heart-wall are mentioned by Bles, who 

 considers that they point to the peritoneal origin of the organ. 

 These occur irregularly, and consist of one or two finely drawn- 

 out cells, much resembling the muscular cells of the heart- 

 wall, to which they are fastened on the one side, whilst on the 

 other they are inserted into projections of the lieart-body, 

 which they have pulled out (Fig. 34). 



The cells, which are uniform throughout the organ, are 

 columnar, though when found isolated in teased preparations 

 of fresh tissue they have assumed a spherical shape. It may 

 be inferred from this that their connection and packing to- 

 gether not only induces, but maintains their cubical form. 

 With regard to their granulations, Bles remarks that in 

 hardened specimens they are crowded with green granules, 

 which are also found in clotted blood. The natural appearance 

 of the granules, however, is very striking. There are three 

 kinds in each cell (fig. 25). First there is an irregular homo- 



in which the animal is enwrapped rendering strength unnecessary, that the 

 usual morphological layers are very difficult to recognise. 



