M. N. Pringsheim on the Pairing of Zoospores. 273 



existence of two kinds of zoospores in the same plant seemed 

 to aflford a clue to the discovery of this unknown sexual act. 



The discovery announced in this paper is that of a modifi- 

 cation of the sexual act, forming a link between the known 

 forms of reproduction, and showing that the different sexual 

 products are a series of variations, passing into one another, 

 of one and the same form. This modification is here called 

 " pairing of zoospores ;" and the essential difference between 

 this and other processes of reproduction lies in the appearance 

 of motile brood-spheres*, which are externally just like the 

 zoospores. 



The plant in which this modification occurs is Pandorina 

 Morum, a plant the different states of which have given rise to 

 a number of gi-oundless and confusing genera, and which is 

 often confounded with another nearly alliedYolvocme, Eudorina 

 elegans. 



Until the appearance of the phenomena introductory to re- 

 production, the plants are distinguishable by the form and 

 aiTangement of their green cells. Pandorina has somewhat 

 wedge-shaped cells. The base of the wedge is tmiied out- 

 wards ; and the cells, which are in close connexion with one 

 another, entirely fill the oval cavity which is enclosed by the 

 general envelope of the plant. Eudorina^ on the other hand, 

 has spherical cells arranged in a single layer at the periphery 

 of the envelope, and at regular, almost equal, distances from 

 one another. The structure of the cell is identical in both 

 plants, and similar to that in the other Volvocinece. 



The number of cells in Pandorina is typically sixteen, oc- 

 casionally less, in Eudorina thirty-two, sometimes fewer. 



Asexual reproduction takes place in Pandorina, as in other 

 multicellular Volvocinece, by the fonnation of a perfect young 

 plant in each cell of the mother plant. By the gradual dis- 

 solution of the general envelope and of the special membrane 

 of the mother cells, the young plants become free and escape. 



In sexual reproduction, as in the asexual, the membrane of 

 the old plant swells, and sixteen yomig plants are formed. 

 The young plants, however, are (at least in part) not neuter, 

 but sexual, and either male or female. Whether the mother 

 plant is monoecious or dioecious is difficult to determine, be- 

 cause the male and female plants are externally alike, and can 

 hardly be distinguished with certaint)' during copulation. 

 There is no striking difference in structure between the sexual 

 and asexual plants, although, amongst the former, plants with 



* [It is difficult to translate the German word ''Befruchtirngskugel." 

 It is used to express the spore or globular mass of protoplasm before it 

 has been fertilized by the action of the spermatozoids. — Tr.] 



