243 Prof. P. M. Duncan on Thallophytes 



servation ; their shape is perfect and they have been carbonized. More- 

 over, the cytioplasm, so transparent or minntely grannlar in most recent 

 specimens, is to be recognized in old corals after they have been decalci- 

 fied, and in fossil corals also, in the form of dark linear masses 



The method of entry of the parasites may be studied by examining the 

 outside of the coral, and then making thin sections, both transverse and 

 longitudinal and radial and perpendicular to the surface. In doing this the 

 nature of the minute thread-like green filaments in and on the coral should 

 be noted, and some specimens should be decalcified with them attached. 

 Perfect septa of recent corals, which have not become dry or which have 

 been lately soaked, may often be examined satisfactorily without sections 

 being made, and the network of ramifying tubes may be readily observed 

 in them ; for a coral structure well permeated by its natural medium is 

 much more transparent than the dry section which may be made from it. 



The sections of the hard structures may be examined after being placed 

 on sHdes (a small quantity of Canada balsam being used to cause them to 

 adhere) without any covering ; and the decalcified specimens, after being 

 washed in water, may be mounted in cells with glycerine. 



E-eflected light may be used satisfactorily with a low magnifying-power 

 in examming the dry section ; for it exhibits the remarkable silvery appear- 

 ance of the bundles of miimte filaments as they enter the theca of the 

 coral, each filament being tubular and refractive. 



A magnifj'ing-power of 400 diameters and an achromatic condenser are 

 the most useful appliances m examining transparent specimens and the 

 decalcified structures by transmitted light ; and the ability to see the long 

 tubes of very different calibres perfectly and well-defined, and distinguish- 

 able from the spicula and their intermediate dark edges, is only possible 

 under a well-corrected object-glass. 



The following order of examination should be followed : — (1) The ex- 

 amination of the canals on the inside and in the septa of corals ; (2) the 

 examination of corresponding decalcified specimens ; (3) the examination 

 of the outer structures, so as to determine the mode of entry of the para- 

 sites, hard and decalcified specimens beiug used ; (4) observations should 

 be made in and about those parts of corals where there is much organic 

 basis amidst the sclerenchyma and between the two laminaD of a septum, 

 and the large size of the associated filaments noticed in solid and decal- 

 cified specimens. 



lY. The usual ajjjyearances of Tyincal Parasitic Canals. 



On examining a thin dry section of a coral, made at a little distance 

 from the outside, or on looking through a transparent septum, the para- 



^ The process of carbonization in these deficate filaments and spores may be imitated 

 Tery significantly by placing some of them under the influence of slight heat and pres- 

 sure. A thin glass coyer being put over a mass, and a spirit 4amp flame being held 

 beneath, it will be found that blackening of some of the vegetable structures will ensue, 

 without the application of much or continuous heat. 



