REPRODUCTION. 639 



macrozoospores of Ulothrix) a portion of the protoplasm is 

 extruded in the form of a vesicle from the sporangium at the 

 same time as the zoospores. In other cases of spore-formation 

 a peculiar process has been observed by Strasburger. He 

 finds, namely, that just previously to the division of the spore- 

 mother-cell, a mass of substance, termed the paranucleolus is 

 extruded from the nucleus. 



Passing on to the development of the sexual reproductive 

 cells, we find that in some cases these cells, like the spores, 

 may be directly developed from a somatic cell, as in the case 

 of the gametes of the Spirogyra and of the planogametes of 

 Ulothrix. In Acetabularia the planogametes are developed 

 from a single cell, the resting-spore, which we cannot but 

 regard as being somatic, inasmuch as it represents (p. 632) the 

 entire sexual generation (oophore) of the plant. In not a few 

 cases the sexual reproductive cells appear to be developed 

 from the whole of the protoplasm of the sexual reproductive 

 organ, be it differentiated or undifferentiated ; for example, 

 the gametes of Spirogyra, the oospheres of Fucus. But in very 

 many cases a portion of the protoplasmic contents of the 

 reproductive organ remains unused. Thus, in the develop- 

 ment of the planogametes of Ulothrix and of Acetabularia, 

 a considerable portion of the protoplasm is extruded with the 

 planogametes from the gametangium in the form of one or 

 more vesicles. 



Something similar has been observed in connexion with 

 the development of the antherozoids in the Muscineae and 

 Pteridophyta. When the antherozoid is set free there is 

 attached to its posterior end an appendage which is usually 

 described as a protoplasmic vesicle. Now as to the nature of 

 this vesicle. It has been ascertained that the antherozoid is 

 developed mainly from the nucleus of the mother- cell, the 

 cilia alone being derived from the protoplasm. The vesicle 

 therefore probably consists to a large extent of the unused 

 protoplasm of the mother-cell. But it has been suggested by 

 Dodel-Port, and his suggestion is fully confirmed by the re- 

 searches of Belajeff on the development of the antherozoids 

 of Isoetes and Selaginella, that the so-called protoplasmic 



