KOLLIKER, ON VEGETABLE PARASITES. 185 



not more than thirty-two rays, cases nevertheless occur in 

 which the growth appears to advance still further, although I 

 have not yet succeeded in obtaining good views of such indi- 

 viduals. This form of fungus might, as I am informed by my 

 colleague, Professor Schenk, constitute a new genus ; but I 

 willingly leave this to the botanists. 



In the scales of living Ganoid fishes, in many of those from 

 fossil genera belonging to this division, which have been 

 placed at my disposal by Professor Williamson, as well as in 

 the scales of Teleostei, I have up to the present time in vain 

 sought for fungus-filaments, although it would seem, at any- 

 rate from Mr. Rose's researches, that they do prevail to a 

 certain extent in these organs also. 



This is the extent of my present researches. Taken 

 together with those of Wedl, which have also been extended 

 over a certain number of fossil molluscous shells, they serve 

 to show that in any case the occurrence of vegetable parasites 

 in the hard structures of animals is very frequent, and that 

 this phenomenon must henceforth take its place among the 

 certain acquisitions of science. Nevertheless, with respect to 

 particulars, much remains to be ascertained, and I would 

 direct attention principally to the following points. 



1. The parasitic growths are very frequent in marine 

 animals, whilst they are almost ivholly wanting in those 

 belonging to fresh water. In the latter, they have been 

 noticed only in Cyclas (Carpenter), Neritina fluviatilis 

 (Claparede), in the scales of an undetermined fish (Rose), 

 and in Neritina croatica and Melania Hollandrii (Wedl) ; 

 whilst in five fresh-Avater bivalves and eight gasteropods 

 examined by Wedl, these growths were absent. The reason 

 of this is not clear. It is either to be sought in the circum- 

 stance that the appropriate lower plants occur only sparingly 

 in fresh water, or that such a difference exists in the con- 

 ditions of vegetation of the two kinds of plants, that those 

 belonging to fresh water are incapable of disintegrating the 

 hard parts in question. But this is an inquiry whose answer 

 may properly be left to the botanist. 



2. Among marine animals also, the parasites are not found 

 indiscriminately in all. In the mollusca they are indeed so 

 abundant that it would almost appear that it is only by 

 chance that they are absent. Nevertheless it seems, as has 

 already been noticed by Wedl, that a thick periostracum and 

 the prismatic layer present difficulties to the penetration of 

 the mycelium which, in many cases, it cannot get over. 

 Moreover, the parasites are absent in chitinous structures 

 almost without exception, especially in those that are less 

 calcified (Decapods). In the strongly calcified forms also, 



