144 W. H. HARRIS ON MARINE MICROSCOPIC VEGETABLE ORGANISMS. 



Gerieral Description. 



These vegetable organisms are chiefly found in fragments of 

 Molluscan shells and Foraminifera, more sparingly in calcareous 

 spicules and particles of Polyzoa ; occasionally they may be 

 detected in spines of Echinoderms. 



Sometimes the superficial layers of one or both sides of the 

 shell are alone infested with the plants; in other cases they 

 penetrate to a considerable depth, or may actually perforate the 

 shell, commencing their growth on one side and passing, either 

 obliquely or directly, through to the opposite side. In the 

 multiplication of individuals of some Lacunae, I have observed 

 an alternation from one side to the other ; but however they 

 behave in this respect there appears to be one essential condition — 

 this is their constant demand for contact with the surrounding 

 water. They appear to satisfy this in more ways than one. 

 They may erode the shell at the point of entry until quite a large 

 cavity of irregular shape is formed ; these may be repeated at 

 intervals, and ultimately becoming confluent, leave the surface of 

 the shell channelled with the form of the plant. Or they may 

 produce short tubular processes equal in diameter to the parent 

 filament, and leading directly to the surface of the shell. In 

 some species these openings are placed very closely together and 

 present a uniform appearance, in others they occur more sparingly. 

 Other species produce very fine hair-like processes upon that 

 portion of filament which hes nearest to the surface of the shell ; 

 innumerable ducts are thus formed to satisfy the requirements of 

 the organism. In other species the method of meeting the 

 demand for contact with water is not apparent, as no specialised 

 organs exist, nor can any apertures be seen ; these are rather 

 deeply immersed in the containing fragment, and further in- 

 vestigation is necessary to solve the mystery. In other species, 

 again, which occupy a more superficial position, the explanation is 

 tolerably easy, as some of these organisms have the power to 

 partially disintegrate the enclosing body beyond the limits of the 

 filaments ; this partial breaking-up of the surrounding parts 

 sometimes presents a cloudy appearance following every detail of 

 the plant's growth ; thus innumerable minute fissures surround 

 them, which efficiently supply the needs of the organism. I have 

 a specimen which has been mineralised, and subsequently decalci- 



