172 K.OELIKEK, ON VEGETABLE PARASITES. 



of vegetable parasites iu the interior of the hard tissues under 

 examination. 



I was at once reminded of the observations of Bowerbank, 

 Carpenter, Rose, and Claparede, respecting the occurrence 

 of peculiar tubes in the shells of Lamellibranchs, and of 

 Neritina, and in fossil fish-scales; and which tubes had 

 also been regarded by the two last-named authors, as of 

 parasitic origin. I found also, on comparison with the pre- 

 parations of shell for which T have been indebted to Dr. 

 Carpenter, that the canals observable in them also belonged 

 to the same category. 



These circumstances, and further investigation, carried 

 as far as I was able, gradually opened up a wide circle of 

 facts and appearances, at any rate of such importance as to 

 induce me not to delay their publication, though still in- 

 complete. 



First and foremost, it is in any case, physiologically, a cir- 

 cumstance of no little interest, to learn that even such hard and 

 compact structures as corals, shells, the scales of fish, and horny 

 skeletons of sponges are bored and frequently pervaded in 

 an incredible manner by lower forms of plants ; in fact, as I 

 would at once remark, by fungi. And here the question — 

 not easily to be answered — arises as to the means by which 

 these organisms are enabled to remove or displace the car- 

 bonate of lime and the organic substance of the tissues thus 

 invaded. But besides this, the correct knowledge of these 

 phenomena is of importance to zoologists, who would thus be 

 protected from great errors in the explanation of the struc- 

 tural conditions of the hard tissues in question. It is well 

 known that Carpenter, under the term " tubular structures," 

 has designated as a special histological formation in bivalve 

 shells, those portions which contain tubuli — a notion which 

 has obtained pretty general acceptance, and which has been 

 combated by no one (vid. Quekett, ' Histol. Catalogue,' vol. i ; 

 Leydig, ' Lehrb. d. Histol./ p. 108 ; ISiebold, 'Comp. Anat.'), 

 and which I have myself also adopted in my memoir upon 

 "Pore-canals and Cell- secretions," at least as respects cer- 

 tain genera. At the same time, however, I have always ex- 

 cepted the horizontally spreading and anastomosing systems 

 of tubes, with respect to whose true nature I have invariably 

 reserved any expression of opinion. But it is now clear, 

 that when the parasitic nature of certain systems of canals 

 in shells is established, as is aetually the ease, the occurrence 

 of a true "tubular structure" is at oner brought into ques- 

 tion; and the same may be said also with respect to the 

 allied conditions iu other hard tissues. With regard to the 

 tubuli in the skeleton of the stonv corals, seen, so far as I 



