340 Proceedings of the Royal Society of Edinburgh. [Sess. 
ochracea, so that the whole structure becomes in a similar manner greatly 
swollen out, being sometimes, in consequence of this conidia-formation, 
double its normal thickness (Plate II.). I am in possession of the main 
facts of the life-history of this organism, which I intend to publish later. 
I may here note that its life-history very closely resembles that of 
Leptothrix ochracea and its allies. 
3. Leptothrix Meyeri (Ellis). — Whilst I am in possession of the salient 
facts in the life-history of the two preceding forms, with regard to this species 
and the two that follow I can only record their presence in the iron-waters 
of Scotland, and hope that I shall later be fortunate enough to find a sample 
in which one or other of these three preponderates. This third species, in 
its general characteristics, is very similar to Leptothrix ochracea (fig. 3, 
Plate III.), and differs from it in an entire absence of shapely-contoured 
walls, and in the nature of the iron deposit, which is at first very 
Fig. 3 . — Leptothrix Meyeri. Dark excrescences indicate spots which have already 
become opaque. 
transparent, so that the walls are easily visible even though the thickness 
of the individual, owing to the deposit of iron, has been trebled. Later, 
the density of the deposit gets greater, and consequently the individuals 
become more opaque. The threads measure from 2/x to 3 fj. in breadth, and 
in length from 40/x to 70 ; u, and, exceptionally, still longer threads may be 
noticed. The transparent nature of the deposit is probably due to the 
presence of a large amount of mucilage outside the walls, formed by the 
degeneration of the latter. The iron penetrates this mucilage, gradually 
colouring the latter, and thus rendering it visible. As the amount of iron 
increases, naturally the transparency decreases. 
In the case of Leptothrix ochracea , speaking generally, large increases 
in thickness are due to the laying down of iron in the spaces between 
the numberless conidia that have been formed, but in this case the 
thickness of the deposit has nothing to do with conidia-formation. I 
have not as yet been able to observe its methods of reproduction, owing 
