86 NATURAL SCIENCE. 



Feb. 



from its likeness to the inverted head of a common mushroom, 

 resembles, in its earliest fixed stage, the young of the ordinary cup 

 coral, Caryophyllia. This cup-like form may remain solitary and 

 gradually develop into the adult individual, or it may produce buds 

 from its wall, which also develop into individuals and thus combine 

 with the original individual to form a colony. In this way there is 

 often produced a kind of stalk which carries many developing 

 individuals. But after a time these latter become separated from the 

 original stalk and set up for themselves, just as though Brussels 

 sprouts were to fall off from the stalk on which they grew and to finish 

 life as independent cabbages. Here is a difficult}^ : the various cups 

 are joined to the stalk not only by soft living tissue but by solid, 

 calcareous tissue or stereom ; how, then, does this stereoni become 

 divided ? Mr. Bourne finds that the coral is attacked, chiefly in this 

 particular region, by various parasites, notably one of vegetable 

 nature. The borings made by these and the limy matter deposited 

 by them in place of the original stereom, render the junction 

 opportunely brittle. It is, however, hardly likely that parasites should 

 conduct their attacks solely for the convenience of their host, 

 without some predisposing cause. Such a cause Mr. Bourne finds 

 in the degeneration of the soft tissues in this region, and he infers 

 that this degeneration of the soft tissues has some weakening effect 

 on the stereom, whereby it is rendered more liable to the attacks of 

 parasites. Similar changes are seen in shells removed from the 

 influence of living tissue, but it is hard to learn the exact nature of 

 the effect that the proximity of soft parts has on stereom. 

 Mr. Bourne suggests " that the shell or coral is in some way affected 

 by its contact with an osmotic surface, and that after separation a 

 molecular change takes place, involving a re-arrangement of the 

 crystalline structure." In the case of shells, however, it should be 

 remembered that the calcite is deposited in organic membrane, 

 which, it may be assumed, is more readily affected in this manner 

 than would be the case if it were homogeneous as coral stereom is 

 thought to be. It is possible that some such organic substratum 

 may yet be discovered in the coral stereom, and this would render 

 Mr. Bourne's explanation still more credible. 



The vegetable parasite that proves so useful to Fungia is called 

 by Mr. Bourne, Achlya penetrans. Achlya, however, is a genus of the 

 Saprolegnaceae, which are not known to live in the sea, and are in 

 fact always destroyed by salt water. On the other hand, it has 

 been shown that certain green algae infest corals and marine shells in 

 this manner, and we would suggest that the form described by 

 Mr. Bourne is probably allied to the genus Gomontia of Bornet. It 

 seems as though the botanists had kept their researches in this 

 direction a little too much to themselves, and we hope to induce some 

 authority on the subject to retail his knowledge in a future number of 

 Natural Science. 



