208 P. M. DUXCAN ON SOME UNICELLULAR ALG.E 



Both the kinds (a and (j) are usually filled, except in the axis, by a 

 dark granular matter ; and the tubes therefore present the appearance 

 of dark edges with a longitudinal central clear line. The length, in 

 some instances, extended over more than one field of the microscope. 

 Each ends in a cul-de-sac, which in this instance is not swollen out ; 

 and often where there are no cell-contents for a little space the 

 absence of special walls can be readily determined. Usually no 

 origin or ending of the tubes can be seen ; but in a few instances 

 their commencement in dark spots at the margin of the coral-wall 

 can be readily seen (fig. 6). These spots are either not much 

 larger than the tube, or are very much bigger, and are filled with a 

 mass of globules with whose exterior the tubes seem to be continuous. 

 Occasionally small dark pigment-masses with a definite globular 

 shape are in contact with one end of the tubes (fig. 14). The large 

 masses are probably the remains of resting spores or oospores ; and 

 the others are conidia (fig. 3). With regard to the numbers of the 

 tubes p there appears to be no regularity ; in some places they 

 are very widely apart, and in others crowded ; but they never appear 

 to inosculate with others, but simply branch. 



In one or two tubes in the specimens examined there are dark spots ; 

 and in one the calibre is swollen out at one spot. 



y. There are here and there very minute tubes which ramify 

 frequently and in a short space, so as to be very dendritic in 

 appearance ; they are densely black and opaque, and their diameter 

 is about one half that of the other tubes. 



2. More or less globular conidium-like masses are either separate 

 or crowded, and in this last instance often are in linear series, 

 (a) They constitute moniliform bodies (fig. 3), sometimes with 

 tubular projections. (/3) They are in evident linear series, but are 

 disconnected; nevertheless traces of excavations, which probably 

 are relics of old tubes which once contained them, are occasionally 

 visible. 



3. Tubes having a calibre twice as large as the others, or even more, 

 and whose contents are discontinuous, dark and often in the form of 

 the conidium-globule (fig. 8). 



There is a piece of a Brachiopod shell in the matrix within the cali- 

 cular fossa of the coral ; and it shows tubes /3 to perfection ; and 

 they look like so many straight and curved wires (fig. 4). 



The tubes mentioned under section y, and the more or less 

 irregular black spots with which they are continuous, readily receive 

 explanation after the study of the Algae parasitic in the Thamnastrcea 

 from Tasmania (fig. 1), and of Calceola sandalina (fig. 11). 



In the Thamnastrcea the enormous multitude of tubes simulate 

 radiating spicula in appearance, and here and there one or two can 

 readily be traced running into a black mass. This irregular shape 

 produced by the growth of the Alga depends on the special molecular 

 structure of the coral. If the tubes were obliterated by fossilization, 

 and the black spaces, not unlike the lacuna? of bone, remained, 

 the appearance would greatly resemble that of some parts of Oonio- 

 phyllum. 



