31 



at least for a part (Fig. 17a-c, 22a-c). This division always pro- 

 ceeded very slowly; hours, even days passed before one could 

 observe the slightest change in the division-stage. And this does 

 not only count for specimina in ravel-preparations, but also 

 for those that remained in absolutely normal conditions either 

 within or without the tissues of a living sponge grown on cover- 

 glass. It also proved probable to me that the algae, with the 

 different shapes of the single chloroplast (Fig. 12 — 15) mentioned 

 above (pag. 24), are all transitory stages from the alga with the 

 primitive and most occurring shape (in which the chloroplast takes 

 exactly the one half of the body, Fig. 5) into forms witli double 

 chloroplast (Fig. 16, 17), so into stages of division. 



Knowing this, we may compose the following cyclus of develop- 

 ment of the symbiotic algae of Spongilla; we place the primitive 

 and most occurring form at the beginning and at the end : Fig. 5, 

 12—16, 17a— c, 18, 19, 20a— b, 21, 22a— c and Fig. 5 again. 



All illustrations of the symbiotic algae have been made with 

 great care from living specimina, with oil-immersion and in Engel- 

 mann's case. All these stages were found in cultures of the isola- 

 ted algae as well as within the tissues of the sponges. 



I have still got to mention a few points somewhat more at 

 large: 1. The stages of division were by no means always larger 

 than the single ones ; this is clear, for the single forms may greatly 

 differ one from the other as to their dimensions. 



2. I call attention for the eccentric way, in which the sepa- 

 rating wall in a mother cell is formed (Fig. 17b — c, 18, 29c). As 

 one knows, the separating wall in algae, for instance in Spirogyra, 

 is formed by a regular, concentric growth out from the existing 

 cell-wall; the ring, formed in this way, closes more and more 

 towards the middle of the cell, till at last it divides the cell 

 body in two parts. I saw this but once in the symbiotic algae 

 (Fig. 25). In all the other cases the forming took place by eccen- 

 tric growth out from one side of the mother-cell-wall, while 

 the separating wall penetrated more and more into the cell till 

 at last it reached the opposite side (of the mother-cell-wall). It 

 is a phenomenon comparable to the one stated by Treub (57a.) 



