parasitic within recent Madreporaria, 



243 



sitic borings, when present, usually resemble long dark lines mth a lon- 

 gitudiaal and central transparent space. The lines may branch here and 

 there, and usually at a considerable angle, and they often dip out of and 

 come within the focus of the microscope in their more or less long course. 

 They are singularly persistent as regards their calibre, which, always small, 

 is unchanged even in the branches and branchlets. The commonest tubes 

 (for such are these linear and longitudinally luminous appearances) are 

 about from g-gVir -soVu- '^^'^ diameter. They are simple excayations, 

 tubular in shape, and they have no special hard tubular wall. Each con- 

 tains a vegetable filament, consisting of a tubular cell-wall and contents. 

 They are cylindrical, and the breadth of the longitudinal light line depends 

 upon the amount of vegetable material within the tube, upon the shape 

 of the perforation, and the nature of the siu'rounding hard structures. 

 When the cytioplasm of the filament which is within the continuous cell- 

 wall is simply glairy matter, the tubes are often difficult to distinguish, as 

 their whole lumen is transparent ; but when the tubular cell-wall is 

 crowded with granules, the light does not pass at all, and the whole tube 

 appears as a dark line. Between these conditions are many, and which 

 refer to the amounts of granular cytioplasm here and there in the same 

 tube. The aggregation of granules determines the clearness of the lon- 

 gitudinal light line, its loss here and there and its replacement by a kind of 

 moniUform appearance of alternate light and shade (Plate 6. figs. 11-17). 



The parasitic canals, although they often branch out and ramify widely, 

 rarely inosculate with others. 



Another very common kind of canal is seen in the same situations, and 

 also throughout the whole coral ; it rarely pursues a straight course, but 

 bends and curves first on one side and then on the other, and branches, 

 either perfect or stunted, come off from the convexity of the curves, 

 usually directly tangential to them. The stunted branches are short and 

 linear, and give a very marked appearance to the canals, especially when 

 they terminate in a spherical end with or without a branch from it. One 

 of the numerous appearances is that of a straight canal bifurcating at right 

 angles, and the continuation of the original canal assuming the form of a 

 short stunted end just beyond the branching. Sometimes this abrupt 

 termination is enlarged and, moreover, less globular in shape (Plate 6. 

 figs. 16-19). 



Swellings or enlargements of the calibre of the canals are not infre- 

 quent, and they are usually impervious to light. It will be noticed in 

 most specimens of long canals that there is a peculiar wavy outline of 

 their path, the excavations not being absolutely in a right liue but in a 

 series of minute and continuous curves. 



In some specimens the canals are very long ; in others they are short, 

 and every variety may be seen in the same section. The direction which 

 they take, and often their length, depend upon the minute structure of the 

 hard parts of the coral. 



