PARASITIC WITHIN SILURIAN AND TERTIARY CORALS. 207 



generally speaking, were filled either with sand and minute fossils of 

 the same period as the mass, or with crystalline carbonate of lime. 

 The specimens were very perfect and had not been rolled. 



In investigating these parasitic growths and perforations in recent 

 and fossil specimens, it is necessary to use thin sections for transmitted 

 light ; but a thick section often exhibits the refractive tubes when 

 reflected light is employed. The sections of the fossils should be 

 carefully made, and scratches on their surfaces noted ; and in order 

 to prevent erroneous interpretations, it is as well not to record any 

 tubes as parasitical in their formation unless they contain matters 

 resembling more or less those of the recent forms, and unless they 

 can be traced in and amongst the normal tissue, and not only on the 

 surface. 



The best plan is to examine, first of all, that part of the section of 

 the coral or shell which was formerly exposed to the sea ; there it 

 is exceptional not to find one or more straight dark lines passing 

 from close to the external margin or old surface inwards at different 

 angles (fig. 6). (A magnifying power of 350 linear is necessary, and 

 careful and good illumination and definition.) When they are satis- 

 factorily seen it is necessary to examine them throughout their length, 

 and to establish, if possible, their relation with others and with the 

 outside, and to notice their contents. 



These perforations or tubes, and the concavities and little loculi 

 with which they are often connected at the surface, cannot be mis- 

 taken for CZicma-borings ; for these last are larger, contain spicules, 

 and do not present the long and often tubular branchings of the 

 vegetable parasites, which, moreover, never contain spicula. But 

 the loculi, when some of the Algae get into the corals, do often 

 resemble the results of the early efforts of Cliona to perforate ; and 

 it is quite possible that the Alga3 may have subsequently occupied 

 the space where a Cliona had been at work ineffectually. 



Their length, minute size, and general characters separate them 

 from some very ill-defined organic perforations seen in Belemnites and 

 modern shells, and which Fischer* and Quenstedt have termed 

 Dendrince. It is hardly necessary to suggest that the edges of the 

 planes of crystallization in no way resemble the tubes. 



Appearance of the tubes and other parasitic productions in Gonio- 

 phyllum pyramidale (Plate XVI.). — The microscopical elements to 

 be observed, are : — 



1. Tubes which have no proper wall, and which are excavations 

 out of the coral-structures. They are found (a) just beneath 

 the surface, running parallel to it ; but these are rare (fig. 2) ; (/3) 

 running more or less inwards at different angles to the surface, 

 many being found Dear to the edge of the coral- wall, and a few far 

 away towards the interior (figs. 6 & 9). These last-mentioned 

 tubes do not vary much in size, and average in diameter about 

 0-008 in. Their calibre does not alter in different parts of their 

 course, which is rarely curved, usually straight, and occasionally 

 branching, the branches being often as large as the parent tube. 

 * Fischer, ' Comptes Rendus.' Dec. 6, 1875. 



Q. J. G. S. No. 126. p 



