ORGANIC PARTNERSHIPS OR SYMBIOSIS 



169 



chlorophyll, which is a characteristic and fundamental important sub- 

 stance of assimilating plants, until Geza Entz and M. Braun demon- 

 strated that the green did not belong to the animal at all, but to 

 unicellular green Algae, so-called Zoochlorellse, which are embedded 

 in the endoderm cells of the polyps in great numbers (Fig. ^^, zchl). 

 As these algoid cells assimilate, and thus liberate oxygen, their presence 

 is of advantage to the polyp. That — as was at first believed — they 

 also yield nourishment to the polyp I consider very probable, not- 

 withstanding the apparently opposed results of the experiments of so 

 acute an observer as von Graff, for I have seen a large number of these 

 animals thrive for months, and multiply rapidly by budding in pure 



ect St ent 



zckl 



Fig. 35- Hydra viridis, the Green Fresh-water Polyp. A, the entire animal, greatly 

 enlarged. Jlf, the mouth. <, tentacles, sp, testis. o», ovary, Ijoth in the ectoderm. Ei, a. 

 ripe ovum, already green, in process of being extruded. After Leuckart and Nitsche. 



B, section of the body-wall, about the position of the ovary in A. Eiz, the ovum 

 lying in the ectoderm (eci), in which zoochlorellse (schl), belonging to the endodei-m 

 (c»*), have already migrated through the supporting middle lamella {st). eik, nucleus 

 of ovum. After Hamann. 



water which contained no food of any kind. In favour of this view, 

 too, are some observations, to be cited presently, on unicellular animals, 

 in regard to whose nourishment by the zoochlorellEe living within them 

 there can be no doubt at all. 



The little algse on their part find a peaceful and relatively secure 

 abode within the polyp, and they apparently do not occur outside of 

 it, at least they do not now migrate from outside into the animal, but 



