ORGANIC DEPENDENCE AND DISEASE 
83 
sites lias been very obvious to tlie writer in liis studies of 
twenty-five years ago on the intimate structure of the shell 
in the ancient brachiopods. In brachiopods, wherever the 
secondary change in the shell substance has been so gradual 
as to cause no disturbance of the fibrous tissue and of the 
vertical perforation which is normal to much bracliiopod 
shell tissue, these vagrant filamentous tubes are readily 
recognized and often evident. Such borings are exceed- 
ingly abundant in the Devonian corals. If they have been 
less often seen in the acephalous mollusks it is perhaps be- 
cause the secondary shell substance is less perfectly re- 
placed. I think paleontologists who have given their at- 
tention to such microscopic structures would be well agreed 
that, for the brachiopods and corals at least, objects which 
presented freest opportunity for attack, these riddling 
algae were far more abundant in the Devonian than in the 
Silurian and Ordovician ; though the evidence of their 
abundance even in the Lower Ordovician sea under con- 
ditions in which hematite iron is segregated in shoal waters, 
has been given by Hayes 1 who, with the approval of Gil- 
bert Van Ingen and W. 0. Howe, refers them to the blue- 
green algae. The existence of such algal borings in the 
scales of cretaceous fishes has been recorded by Wedl 2 and 
by Rose. 3 The heavy plates of the Devonian fishes would 
seem to have afforded favorable conditions for such opera- 
tions but they have not thus far been searched. 
We have no clew at all to the inception of this very ex- 
traordinary adjustment or of the mode of acquirement by 
the filamentous plants of the singular property of dissolv- 
ing or otherwise excavating their tubes in hard organic 
lime deposits. How the work is done by the plant is still, 
amid various suggestions of chemical and mechanical ac- 
1 A. O. Hayes. The Wabana Iron Ore of Newfoundland: Canadian Dep ’t 
Mines; Geol. Survey, Mem. 78, p. 75, pi. 1. 1915. The colored plate shows 
coiled tubules in the nucleus of the iron spherulites. 
2 Wedl. Op. cit. 
s C. B. Bose. Trans. Microscopical Soc. London, n.s., v. 3, p. 7, pi. 1. 1855. 
