424 ANNUAL REPORT SMITHSONIAN INSTITUTION, 19 3 5 



decorating the backs of turtles belong to the two species Basicladia 

 crassa and Basicladia chelonuin. 



Algae grow commonly on the long, thick hairs of the dense coat of 

 the three-toed sloth in the Tropics (pi. 2, fig. 3). This animal loves 

 the coolness and the shade, which it seeks in the tops of trees, thus 

 furnishing ideal conditions for the bright green algae growing on the 

 hairs and helping to conceal it among the leaves. Large numbers of 

 minute microscopic unicellular algae grow in dense colonies in the 

 crevices of the elongated scales that, under the microscope, are seen 

 to lie singly overlapping the hair shaft. Two genera of algae have 

 been described that grow on Bradypus^ the three-toed sloth, and on 

 GJioleopus^ the two-toed sloth ; they are the green alga Trichophilus 

 toelckeri and the red alga Cya;nodernia hradypodk. Here at the 

 Smithsonian Institution, in the collection of skins of the division of 

 mammals in the United States National Museum, I have abserved 

 the algae in a dried green condition on hairs of sloths from Costa 

 Rica that were killed 60 years ago. 



Algae may also cause harm or injury to the plants or animals on or 

 within which they are growing. The alga Nostoc penetrates through 

 the stomata of the tissue of certain liverworts, then breaks up and 

 destroys the neighboring' cells of the host plant as it makes its exit 

 through the tissues of the host. Nostoc also grows in the spiral fila- 

 ments of Sphagnum moss. Hydrodicfyon, the alga commonly known 

 as the water net, has been found about an unlucky dead fly, which it 

 had undoubtedly entrapped. Filaments of an OsciUatona have been 

 found growing within the intestinal epithelium of the carp; also 

 colorless algal parasites have been found in the caecum of the guinea- 

 pig, the pharynx of the hen, the mouth of the horse, pig, sheep, and 

 goat, and in the intestines of man. As an adaptation to parasitism 

 these algae lose their chlorophyll, since their food is supplied them in 

 the desired form without the necessity of their manufacturing it 

 themselves. 



The great fondness of some algae for calcium makes all shell- 

 bearing animals open to attack from the calcareous or perforating 

 algae. Often on the seashore, we find shells covered with little gray 

 and green spots like the spotted petals of the guinea-hen flower. 

 These little spots are not only on the surface of the shell but extend 

 deep into it until the shell sometimes is corroded completely by the 

 ramifications of these calcium lovers. The same alga, Siphonocladus 

 voluticola, often responsible for this destruction, is found in both 

 salt water and fresh water. 



These perforating algae are found from the cold seas of the north 

 to the extreme south of Cape Horn, in all the European seas, on the 

 eastern and western coasts of America, and in the Tropics of Africa, 



