430 Mr. Lawson Tait on the 



Koster regards these two forms of cells'as the same, and differing only 

 in position. But he has evidently neither applied high powers no; 

 delicate stains to them, so as to discover the presence of a nucleolus in 

 one and its absence in the other. The different actions on them of litmus 

 and hematoxylin seem very decisive as to their being different structures, 

 and probably having different functions. They are also quite different 

 in size and appearance. 



Koster states that he has seen the nuclei of the lacunae send fine shoots 

 into the branching canals. This is only an optical delusion, which is 

 dispelled by the use of the high power immersion-lens-. 



I conclude, therefore, that the proper tissue of the cord is entirely 

 canalicular. How the canals are formed, and what relation their nuclei 

 have to their growth and nutrition, has yet to be determined. It is, of 

 course, more than probable that the explanation of the growth of the 

 stellate corpuscles advanced by Virchow, Aeby, and Eberth is applicable 

 to the lacunar canals ; that is, that they are the result of cell modifica- 

 tion, the body of the corpuscle expanding into a membrane for the 

 formation of the lacuna and its processes, whilst the nucleus remains 

 for nutritive reproduction. This, however, I am not yet prepared to 

 accept, but it might explain one function of the round cells. 



Koster speaks of having seen " in silver-stained sections irregular or 

 interrupted lines showing through the white canals, which remind us of 

 the luting substance between two epithelial cells ; " but I have not been 

 fortunate enough to have seen any of these lines. 



I agree with Koster that it is probable that the canals communicate 

 directly with the amniotic cavity by means of the stomata ; but, bej^ond 

 having satisfied myself that the stomata lead directly into the layer of 

 canals immediately under the epithelium, I cannot say I have traced the 

 continuity. I believe the minute streams of injection-fluid, which both 

 Koster and I have seen flowing from the surface of the injected cord, 

 have come from the stomata, but I have not yet caught the fact in a 

 section. Koster makes a similar confession. 



In one point I am in disagreement with all observers with whose work 

 I am acquainted, in that I am certain that the nuclei of the lacunae are 

 not loose in the cavities but are adherent to the wall at one point. The 

 double method of injection and staining proves this conclusively. 



By no kind of process which I have employed, in quite a large number 

 of observations, have I been able to discover any thing in the least degree 

 resembling a nerve-fibre in the substance of the cord ; and I have failed 

 to substantiate Kolliker's observation of the entrance into it of branches 

 from the hepatic plexus. 



When one of the columns of the cord is injected the canals will be 

 seen, as I have already said, to run up to the muscular walls of the 

 blood-vessel of the column, but I have never seen a canal enter the mus- 

 cular tissue. 



