NO OPEN CONNECTION 431 



its very end, the "blind end" of dcMan, and that the freely moving con- 

 tents of the tube are visible clear to what might be called the surface tissue 

 of the intestine (tissue of the intestine altered, to be sure). DeMan's figure 

 25 seems easily to admit of this interpretation. I find the cells of the wall of 

 the intestine (if they be really intestinal) are altered where the vessel is 

 attached, and this fact suggests that we have here modified selective tissue 

 the osmosium, the function of which is to extract from the intestine and 

 usher into the demanian system, presumably mainly by osmosis, a product 

 utilized by the latter. 



May not the evidence offered by zur Strassen for an open communication 

 between the enteric efferent and the intestine in pristiurus, i.e. the evidence 

 of his microtome sections, be capable of a different interpretation? Could 

 zur Strassen's sections have been deceptive? The published figures of his 

 "open connection" between the demanian system and the intestine are not 

 satisfying, in that they appear to show a large portion of the cell walls missing. 

 Now pristiurus ingests mud, and, in consequence, its intestine normally 

 contains much fine grit. Is it not likely that this grit, acting as it naturally 

 would during the sectioning, would damage, or even destroy, delicate cells 

 that, before being broken, might have closed the aperture which zur Strassen 

 shows and describes as an open connection? The suggestion is that this might 

 occur, at the time the sections were cut, through the combined abrasive 

 action of the grit and the coincident dulling of the microtome knife. All 

 zur Strassen's figures show the intestinal lumen more or less open; but when 

 the intestine is entirely empty and free of grit it is collapsed, not open, so that 

 the lumen, in well made sections, is closed and difficult to see. May not this 

 indicate that the vacant lumenal spaces shown in zur Strassen's illustrations 

 probably did contain grit at the time of fixation, and hence, no doubt, at the 

 time of sectioning? 



Pristiurus, fuscus and some other mud-inhabiting Oncholaims can be kept 

 alive in pure running sea water for days, or even weeks, and when so kept 

 evacuate the intestine very completely. Sections may then be made without 

 the interference of the grit normally present in the intestine. / have not found 

 such sections to present the appearance figured by zur Strassen. 



In an examination of very many specimens, alive and sectioned, I have 

 never been able to convince myself of the existence of an open communication 

 between the intestine and the demanian system. 



Any such open connection would seem a grave menace to the well-being 

 of the organism. For if the enteric intake were of the nature figured and 

 described by zur Strassen, there would seem to be little or nothing to prevent 

 the entrance into the demanian system of undigested detritus contained in 

 the intestine, together with numerous living microorganisms which normally 



