244 DESCRIPTIONS OF PREPARATIONS. 



chlorophyl bodies of plants multiply by fission. It may be added that Hydra 

 viridis, unlike Spongilla, when confined in the dark, does not lose its colour, 

 and that in some varieties green angular bodies have been found similar to the 

 colourless angular bodies of H. fusca. 



With reference to Vortex viridis, von Graff states that green-coloured examples 

 were observed by him to give origin to colourless young ; that green examples, 

 confined in the dark, became colourless in seven days. He also states that the 

 green Mesostoma viridatum sometimes occurs almost devoid of chlorophyl coloured 

 cells. These facts, according to him, point to the algal nature of the green 

 bodies in these animals, and raise a similar presumption with reference to Convolnta 

 Schultzii. 



As to the physiological side of the question, it has been proved that, under 

 the influence of light, oxygen is given off by the yellow cells, as well as by most 

 animals of a green colour, by Hydra among the number. 'Spongilla and Vortex 

 viridis do not seem to have been investigated in this respect. Starch also is 

 formed in the yellow cells ; in the chlorophyl bodies of many Protozoa ; in the 

 cells of Spongilla, but not in intimate connection with the green bodies ; in the 

 green cells of Convoluta Schultzii, while glycogen in plenty occurs in the colourless 

 mesoderm cells, internal to the layer of green cells in this animal. It has been 

 detected also, but not often, in the protoplasm of the endoderm cells of Hydra 

 viridis. Starch vacuoles, however, it must be added, are found in colourless 

 Spongillae in as great abundance as in those of a green colour. 



The theory of symbiosis is that, while the animal supplies carbonic acid, and 

 probably nitrogenous matters to the alga, the latter, under the influence of light, 

 yields a supply of oxygen, of starch, and possibly other substances to the animal. 

 Brandt's experiments appear to prove that those species of Sea-Anemones which 

 contain yellow cells can get a supply of oxygen and of food from the algae, and 

 live at least for a longer time under circumstances in which the same species 

 speedily die if deprived of their yellow cells by confinement for a time, e. g. eight 

 weeks in the dark. Convoluta Schultzii, according to Geddes, seeks the lightest 

 spots, and can live without food if exposed to light for four to five weeks. And it 

 has been noted that many green Infusoria and Radiolaria containing yellow cells 

 appear not to require any food supply ab extra. The fungus in the lichen appears 

 to play the part of an animal, and it is supposed that the mycelium surrounding 

 the rootlets of the oak, &c., acts as an intermediary between a rich soil and the 

 rootlets. The subject of symbiosis, however, is one involving many difficulties, 

 and a student who consults the literature of the subject will find discrepancies in 

 the accounts given by different observers. The literature is a large one, and the 

 sketch given above, the barest outline. 



Die Actinien, Hertwig (O. and R.), J. Z. xiii. 1879 (also separate, as pt. i. of 

 Studien zur Blattertheorie, Jena, 1879). Actiniaria, Hertwig, R., Challenger 

 Reports, vi. 1882. Le Attinie, Andres, Fauna und Flora des Golfes von Neapel, 

 ix. pt. i. 1882. Deep-sea and Pelagic Actiniae, Moseley, Tr. L. S. (2) i. 1879. 

 British Sea Anemones, Gosse, 1860. 



Cereanthus, Von Heider, SB. Ak. Wien, Ixxix. Abth. i, 1879. Edwardsia, 

 Andres, Mitth. Zool. Stat. Naples, ii. 1881. Various genera, Jourdan, A. Sc. N. 

 (6) x. 1879-80. 



