448 M. J. Brock on the 



that the old supposition that tlie chlorophyll is uniformly 

 diftused in the j)rotoplasm in the unicellular Algai is erro- 

 neous ; on the contrary, according to him all true Algai have 

 formed chlorophyll- bearers. We cannot abstain from men- 

 tioning this memoir at any rate in passing, as our own obser- 

 vations agree so well with it ; moreover it is known that in 

 the majority of the green corpuscles found in animals the 

 chlorophyll is localized in special chlorophyll-bearers. The 

 question whether the green cells of Tridacna are true uni- 

 cellular Alga3 or only developmental stages of them must be 

 very superfluous when even the vegetable nature of these 

 structures cannot be established with perfect certainty. Upon 

 this point it may be noted here en passant that the latter 

 opinion, put forward by Geza Entz, on account of which 

 Brandt gave up his generic name Zoochlorella, has recently 

 been disputed by Klebs * in the most decided manner. And 

 it cannot be denied that of the diagnosis which Klebs {loc. 

 cit. p. 382) gives for the genus Pleurococcus much is applic- 

 able to the green cells of Tridacna ; but we need hardly say 

 expressly that we will not therefore announce the latter as a 

 new species of Pleurococcus f. 



The place in which we find the green cells in Tridacna is 

 unusual. The ordinary locality of the vegetable symbionts 

 is in the tissue, i. e. the cells of the host ; hitherto they have 

 only rarely been found floating freely in the cavities of its 

 body. If we interpret Brandt's expression correctly (see 

 p. 447) Elysia viridis is also in the same case ; in the Ephyrte 

 of Cotylorhiza^ Glaus found chlorophylloid Algge freely floating 

 in the gastrovascular space J ; Chun refers to yellow cells n\ 

 the vessels of Velella § ; and Sillimnn saw Alga? deposited in 

 the intei cellular spaces of the body-parenchyma in a North- 

 American freshwater Turbellariau, Mesostoma vlviparum, 



* G. Klebs, " Ueber die Organisation einiger Flagellatengruppen iind 

 ihre Beziehuugen zu Algeu uud lufusorien/' in Uuters. botau. Inst. 

 Tubingen, Bd. i. p. 2:33. 



t At any rate, as Prof. Graf Solms baa likewise bad tbe goodness to 

 point out to me, tbe green cells of Tridacna are quite different from tbose 

 of otber classes of animals if only by tbe great number and spherical form 

 of their cbloropbyll-bearers. Ibe green cells of Hydra bave a single 

 bood-like cbloropLiyll-bearer, and increase by tetrad-formation (see, for 

 example, tbe figures given by Hamaun, Zeitscbr. f. wiss. Zool. Bd. xxxvii. 

 Taf. xxvi. figs. 4-7), as also tbose of tbe Infusoria. 



X C. Claus, " Die Epbyren von Cotylorhiza und HMzostoma und ibre 

 Eutwicklung zu acbtarmigen Medusen," in Arb. Zool. lust. Univ. Wien, 

 Bd. V. 



§ C. Cbmi, " Ueber die geograpbische Verbreituug der pelagiscb- 

 lebeudeu Seetliiere," in Zool. Auz. 1^86, no. 215, p. 72. 



