1883-84-] Edlnbui'gJi Natiiyalists Field Club. 175 



Bonellia viridis, the Antliea green of Anthea cereus, the Crustacea 

 green of Palaimon viridis, and the Pentacrinin of Pentacrinus — this 

 last named pigment changing from a green to a purple hue on acidi- 

 fication. Yet green pigment of functional value equivalent to 

 chlorophyll is aj)parently sometimes developed by true animal pro- 

 toplasm ; while, on the other hand, greenness in animals may be due 

 to the existence of green or greenish-yellow plant organisms existing 

 inside the animal tissues, in which case we have the curious phe- 

 nomenon of an animal and a plant agreeing to live together, and, as 

 we shall see below, " reciprocally accommodating " one another from 

 a physiological standpoint. These organisms are said to be Syjn- 

 biosists, Commensalists, or Mutualists. 



It is at this stage to be remarked that of this association of one 

 organism with another we find many illustrations, differing at once 

 in kind and in degree. The simplest type is perhaps represented by 

 cases where the guest is external and the host is entirely passive. 

 Thus we find Diatoms epiphytic on Algse; Lichens, Alga^., or Mosses, 

 on trees ; Alga3 epizoic on Snails, or even on the more active Cyclops 

 and Daphnia ; while the list of Seaweeds found growing on other 

 Algte is a very large and comprehensive one, although the precise kind 

 of this association — whether wholly or partially epiphytic or wholly 

 or partially parasitic — is not in all cases clearly determined. In 

 addition to the fact of association of plant with plant, we find similar 

 associations of animal with animak Thus the Commissioners on the 

 Fisheries of New South Wales, in a report published in December 

 1883, remark that "the very young fry of Trachurus trachurus have 

 a most extraordinary and ingenious way of providing for their safety 

 and nutrition at the same time. They take up their quarters inside 

 the umbrella of the large MedusiB, where they are safe from their ene- 

 mies, and are, without any exertion on their part, supplied with the 

 minute organisms Avhich constitute their food, by the constant current 

 kept up by the action of the curtain-like cilia of the animal." In 

 Fol's 'Recueil Zoologiqiie Suisse,' vol. i. (1883), pp. 65-74, a similar 

 association of Caranx melampygus and Crambessa palmipes is re- 

 corded froni the Mauritius. Annelid tubes, too, have been found 

 surrounded by the corallum of PoritidcB and other coralline zoophytes. 

 On the other hand, there are associations of organisms in which both 

 host and guest are active and mutually lieneficial to one another, as 

 in the case of Anthea, Lichens, &c., to be referred to below. 



The distinction between Commensalists and true parasites, such as 

 the Dodder, Peronospora and other Fungi, Taeniae, Trachina?, 

 OxyuridtC, &c. — all of which exercise a deleterious function npon 

 their host — was first draAvn by A"an Eeneden, Avho explained the 

 phenomenon of Commensalism by a " sympathy " existing between 

 host and guest. Eut, more recently, Mr Geddes (' Proc, Eoy. Soc.,' 

 Lond., 1879), by submitting a number of green Convoluta Schultzii 



