Dr. Daivsoii's * Dawn of Life.'' 365 



parallel to each other, and often slightly bulbose at the ex- 

 tremity. Fibrous serpentine, on the other hand, appears as 

 angular crystals, closely packed together, while the numerous 

 spicular crystals of siliceous minerals which often appear in me- 

 tamorphic limestones, and may be developed by decalcification, 

 appear as sharp angular needles usually radiating from centres 

 or irregularly disposed. Their own plate (Ophite from Skye *) 

 is an eminent example of this ; and whatever the nature of the 

 crystals represented, they have no appearance of being true 

 tubuli of Eozoon " f- 



After our descriptions, to which Dr. Dawson refers in the 

 extracts just given, were published |, one of us went to the 

 Isle of Skye, where matei'ials were collected for the paper 

 which subsequently appeared § ; while shortly afterwards 

 Dr. Dawson, unacquainted with the latter communication, for- 

 warded to the Royal Irish Academy a paper || (partially reprinted 

 in ' The Dawn of Life ') containing, in addition to several cri- 

 ticisms, the foregoing extract. We were thus led to draw up 

 an answer, which is not even alluded to by our opponent. 



Confining ourselves to the point in question, the following 

 is our reply to it : — " We have always admitted that the true 

 cell-wall presents minute cylindrical processes traversing car- 

 bonate of lime, and usually nearly parallel to each other, even 

 hefore Dr. Dawson had published any description of them j 

 and we have throughout persistently used the term aciculi for 

 the ' casts of the tubuli,' by which we wished them to be 

 understood as having a cylindrical form. What is there to 

 justify Dr. Dawson in again repeating that we ' confound the 

 nummuline layer with fibrous and acicular crystals ' ? In our 

 last paper we accepted Dr. Dawson's first description of the 

 * true cell-wall ' as consisting of ' slender undulating threads 



* ' Proceedings of the Royal Irish Academy/ vol. x. pi. xliv. fig. 10. 

 Our description of this figure states that it represents " grains (' chamber- 

 casts ') of pale green serpentine in a decalcified specimen of Liassic ophite 

 from the Isle of Skye, presented to us by Professor Harkness. The gi-ains 

 are for the most part invested with ' true nummuline layer/ which in 

 some places is asbestiform." One of the grains " has its surface quite 

 hispid with separated aciculi." Any one by referring to our figures and 

 description of the Lisoughter " spheroidal bodies " already alluded to, and 

 published in 186G, will observe that they are described as having attached 

 to them " tufts of crystals," the " crystals " being " divei'gent, also sub- 

 parallel." This shows that, had the Isle-of-Skye acicidse been " shai-p 

 angular needles " or " crystals/' they would have been described as such. 

 We never likened these to the '^cell-wall." 



t ' The Dawn of Life,' p. 196. 



\ ' Quarterly Journal of the Geological Society,' vol. xxii. p. 218; and 

 ' Proceedings of the Royal Irish Academy,' vol. x. pi. xliv. fig. 10, p. 641. 



§ Proc. Rov. Irish Acad. vol. i. ser. 2, pp. 132-189. 



II Ibid, vol.'i. ser. 2, pp. 117-123. 



