THE GENUS HYDRODICTYON. 55 



in accordance with a definite plan, so as to make a body of definite 

 shape and size, yet in which cadi cell is an independent being, 

 drawing nothing from its neighbours. The cells themselves are 



cylindrical, with a thickish cellulose wall, and having no nuclei. 

 Their chjorophyllous protoplasm is granular, ami is placed in the 

 exterior portion of the cell, forming thus, within the outer wall, a 

 hollow cylinder, in which are imbedded starch granules, and whose 

 interior is occupied with watery contents. The Hydrodictyon cell, 

 when once formed, is capable of growth, but not of going through 

 the usual process of cell multiplication by division, so that the adult 

 frond is composed of just as many and, indeed, the same cells as it 

 had in its earliest infancy. 



No true sexual reproduction has as yet been discovered in the 

 water-nets. There have been described, however, two forms or 

 methods in which the species multiplies, both of them occurring by 

 means of motile zoosporoid bodies. In the one case these develop 

 immediately into the new plant, whilst in the other, before doing 

 so, they pass through a resting stage. Of the life history of the 

 latter, the microgonidia, I have no personal knowledge. 



The investigation of the production and development of the 

 macrogonidia, however, has occupied considerable of the time 

 devoted by myself to the microscope, and I have seen large num- 

 bers of specimens in almost all the stages of development. I have 

 never been able to detect, however, any decided motion in the 

 macrogonidia. 



They are formed in the protoplasmic stratum already alluded to 

 as occupying the outer portion of the interior of the Hydrodictyon 

 cell. The first alteration in this, presaging their formation, is a 

 disappearance of the starch granules, and a loss of the beautiful, 

 transparent green colour. Shortly after this, even before all traces 

 of the starch-grain are gone, there appear in the protoplasm 

 numerous bright spots placed at regular intervals ; these are the 

 centres of development, around which the new bodies are to form. 

 As the process goes on, the chlorophyl granules draw more and more 

 closely around these points, and at the same time the mass becomes 

 more and more opaque, dull, and yellowish brown in color. This 

 condensation continues until at last the little masses are resolved 

 into dark hexagonal or polygonal plates, distinctly separated by 

 light, sharply defined lines. In some the original bright central 

 spot is still perceptible, but in others it is entirely obscured by the 

 dark chlorophyl. The separation of these plates now becomes more 

 and more positive, and they begin to become convex, then lenticu- 

 lar, and are at last converted into free, oval, or globular bodies. 

 When these are fully formed they are said to exhibit a peculiar 

 trembling motion, mutually crowding and pushing one another, 

 compared by Mr. Braim to the restless, uneasy movement seen in 

 a dense crowd of people in which no one is able to leave his place. 

 Whilst the process just described has been going on, the outer 



