36 COCCOPHYCEJ3. 



to end in such a way as to form polygonal and mostly pentagonal 

 meshes, the size of which varies with the age of the plant. These cells, 

 which are closely conjoined, but have no passage-ways between them, 

 are capable of independent life, so that the Hydrodictyon may be looked 

 upon as an elaborate type of a cell-family, one in which cells are con- 

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

 shape and size, yet in which each 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 chlorophyllous 

 protoplasm is granular, and is placed in the exterior portion of the cell, 

 forming thus, within the outer wall, a hollow cylinder, in which are im- 

 bedded 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, in- 

 deed, 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 macro- 

 gonidia, however, has occupied considerable of the time devoted by 

 myself to the microscope, and I have seen large numbers of specimens 

 in almost all the stages of development. I have never been able to 

 detect any decided motion in the macro gonidia. 



11 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 colour. 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 lenticular, 

 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 A. 

 Braun to the restless, uneasy movement seen in a dense crowd of 

 people iu which no one is able to leave his place. Whilst the process 

 just described has been going on, the outer cellulose wall of the Hydro- 

 dictyon cell has been undergoing changes, becoming thicker and softer 

 and more and more capable of solution, and by the time the gonidia 

 are formed it is enlarged and cracked, so that the room is afforded 

 them to separate a little distance from one another within the parent- 

 cell. Now the movements are said to become more active a trembling 

 jerking which has been compared to the ebullition of boiling water. 

 There is, however, with this a very slight change of space, and in a very 

 short time the gonidia arrange themselves so as to form a little net 

 within the parent-cell, a miniature in all important particulars of the 



