i8 NATURAL SCIENCE. July, 



he examined many recent specimens, from the littoral zone to a depth 

 of 1,095 fathoms, from waters, with a temperature ranging from 

 39*7" F. to 55° F., from Davis Straits southwards. His general 

 conclusions were that the boring tubes are more abundant in a coral, 

 the warmer the sea-water and the less the pressure to which it is 

 subjected, and that " the fossil corals of Silurian age were also 

 affected by closely allied, if not specifically identical, forms." It 

 remained for the Swedish botanist Lagerheim (4), in 1886, and more 

 especially for the French algologists Bornet and Flahault (2), in 1889, 

 to supply an accurate botanical account of the perforating organisms, 

 and to point out their most important biological significance — that 

 of shell destroyers. 



In a paper by Bornet and Flahault, entitled " Sur les algues 

 perforantes," ten genera are described and their life-histories in some 

 cases more or less fully made known. Of these ten, five are new 

 to science, and are confined, so far as is known, to the peculiar 

 habitat furnished by molluscan shells. All the perforating plants 

 agree in their general mode of development. At first they spread out 

 horizontally in the epidermal layer of the shell, forming an irregular 

 network or radiating round a central point. From the horizontal 

 layer branches grow out, some at right angles, penetrating into the 

 substance of the shell, dissolving its calcareous matter as they proceed. 

 Oiher branches elongate themselves, parallel to the primary filaments. 

 As time proceeds, these horizontal filaments become so numerous and 

 their branches so close together, that the intervening calcareous 

 matter of the shell finally disappears, and the plant, now in immediate 

 contact with the surrounding water, is able to send off its reproductive 

 cells. The surface of the shell becomes at the same time rough and 

 irregular. It is to Bornet and Flahault we owe the important 

 generalisation that this constant gnawing away of the shell ends in its 

 complete destruction, and is the chief cause of the disappearance of 

 shells in quiet bays where they are not mechanically destroyed by the 

 ceaseless activity of the waves. 



The boring plants belong mostly to the blue-green algae 

 (Cyanophyceae), and the green algae (Chlorophyceas) ; one is a red 

 alga, two are fungi, and the brown algae are unrepresented. 



The presence of a perforating green plant in a shell is easily 

 distinguished from a mere superficial green deposit of germinating 

 Ulva, etc., by scraping with one's nail, or, better, by breaking the shell 

 in two. If the broken surface shows greenness to any depth, one may 

 be satisfied it is due to a perforating alga. The identification of the 

 particular species present requires, in most cases, decalcification of 

 the shell and microscopic examination subsequently. A good deal of 

 information can often be obtained by examination of the shell 

 untreated, under the quarter-inch objective, or by rough powdering of 

 the shell in a mortar. Many of the fragments thus produced stand on 

 edge when placed on a slide, and can be examined as shell sections. 



