206 P. M. DUNCAN ON SOME UNICELLULAR ALG^E 



believed it to be the Saprolegnia feracc of Kiitzing. He did not 

 examine the corals ; but after satisfying himself about the occurrence 

 of the parasite in recent species, he examined some fossil shells, and 

 detected it (amongst others) in Leptcetia Icevis from the Devonian. 



Thus these investigations showed that there were parasitic vege- 

 table growths in modern corals and in many shells even as old as the 

 Devonian, and that they either were confervas or fungi. 



During the course of some investigations into the minute structures 

 of Tertiary corals, I was greatly puzzled by the omnipresence of a 

 system of branching canals ending in culs-de-sac and having dark 

 borders and a refractive central area. In one instance (in a 

 Thamnastrcea * from Tasmania) the tubes frequently merged into an 

 irregular dark mass, and resembled the tubuli of bone (Haversian 

 canals) passing into lacunse ; and as they surrounded in a circular 

 series a radiating mass of closely approximated normal spicula, the 

 resemblance to a low class of osseous tissue was extraordinary. These 

 canals had their length, direction, and frequency evidently in relation 

 with the situation and regularity of disposition of the denser and 

 normal coral structures : where the spicula were closely united 

 laterally, their extremities radiating from a common centre, the 

 tubes did not pass into, but surrounded the mass ; and when 

 these nodules of normal tissues were in long series the tubes ran 

 down by their sides. Hence sections cut across the calices and 

 septa did not exhibit many tubes, but numerous dot-like markings, 

 which were their cut ends ; on the other hand, sections longitudinal 

 to the septa and costae presented long lines of tubes with ramifica- 

 tions and swellings. The resemblance in shape and size of these 

 tubes to Quekett and Wedl's figures led to the belief that even this 

 hard coral had not been without its parasite, and incited me to 

 follow up the subject in living, recently dead, and other fossil species. 



The results of my work on the recent forms, as they enter especially 

 into questions foreign to those considered by this Society, are about 

 to be presented to the Eoyal Society ; but I thought that a notice of 

 the occurrence of these interesting parasites in such old forms as 

 Goniophyllum and Calceola would be of interest. 



I chose this species of coral and Calceola because their hard parts 

 admit of thin and wide sections, and also because I was working 

 upon them in conjunction with Mr. H. Woodward, P.K.S., in in- 

 vestigating the question of the Rugosa operculata of Lindstrom. But 

 I have examined others also, with different degrees of success. In 

 the specimens which Mr. H. Woodward had had cut, the f ossilization 

 had been very perfect, and much of the calcite had been replaced by 

 crystalline carbonate of lime. The calicular fossa and the cavities, 



* On decalcifying a part of a thin transverse section of this Thamnastrcea, and 

 after careful washing, a yg-in. immersion-lens was used. It showed a basement 

 tissue almost homogeneous, on which were numerous straight and a few rami- 

 fying tubes, resembling in shape the refractive tubes of the perfect specimen. 

 The tubes were such, and not excavations in the homogeneous tissue ; and they 

 had each a proper and hyaline-looking wall ; the contents were more refractive 

 than it and than the surrounding structures. Hence the cellulose wall was 

 preserved during the process of fossilization. 



