ORGANIC DEPENDENCE AND DISEASE 83 



sites lias been very obvious to the writer in his 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 brachiopod 

 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. 



3 C. B. Eose. Trans. Microscopical Soc. London, n.s., v. 3, p. 7, pi. 1. 1855. 



